BEST HARMLESS/SIGNATURELESS SPEAKERS CAPACITORS.

Glad you like them.  I would not paint with the broad brush you use saying all boutique caps are a joke.  I tried Wima and they are nothing special to me.  Certainly no Vcap Odam or Miflex copper foil! 
This is all subjective based on your ears, preferences and particular room and piece of gear the caps are installed in.  
Great when you find something that works for you. 

Over at the Humble Capacitor review site they liked it fine giving it a rating of 8 which is pretty average. Not poor, not great like many “boutiques”.  That jives with my experience with these in both crossovers and electronics.  They are pretty average.  The quote from the Humble site.....

WIMA MKP 10 100VDC - 10% tolerance

Technical specifications (according to manufacturer): "Pulse capacitor. The construction principle of the series WIMA MKP 10 consists of a non-metallized dielectric film and an carrier film metallized on both sides acting as electrode. Thanks to the metallization on both sides, the electrical conductivity is considerably improved and the contact surface between the electrodes and the schoopage layer is doubled. This results in better contact and allows for high current and pulse loading capability. The properties of metallized capacitors such as excellent self-healing and high volume capacitance remain unchanged."

Sound: With the WIMA MKP 10 you get a neutral, smooth and well balanced capacitor. For this price range the amount of transparency is quite reasonable and overall the MKP 10 is pleasant to listen to. Compared to the similar shaped and sized Mundorf RXF the presentation is more forward and a fraction less clear. But never the less it has good overall sound qualities. Don't forget to give it some time to burn-in. Fresh out of the box they sound restricted and dynamics are limited. After several weeks of use they should open-up.

Verdict: 8

You may want to try the new Vcap Odam as they are more neutral than the PIOs you don’t seem to like. They are much more 3D dimensional than the Wima cap and not very big physically.

It sounds like the better caps are revealing some negative sound attributes unique to your system and ears while the Wima caps are masking it.   This would make sense as the Wima caps are not top class in resolution or refinement. That is why I say this can be very subjective based on your system’s sound including It’s relative sonic strengths and weaknesses. 

Dear @grannyring : As a fact the caps in the woofer crossovers are V-caps and in the past I use it in all the speaker crossover drivers.
Sure, I can test the 4.7uf in the tweeters to " see " first differences with the OIMP and after that with the WIMA ones. Chris is a friend and I use too V-caps teflon Cu with very good success.

Normally in audio all is room/system dependent and owner MUSIC/sound priorities, no doubt about.

My system was and follows listened by many gentlemans that are first than all MUSIC lovers and second audiophiles and some music players.

Not only for me but for them the unanimous opinion is that the room/system strength is its very high resolution where there is no place to hide any weak characteristic in any link of the system chain.

A few years ago a friend of mine and me designed and builded a SS active and current drive phonolinepreamp that in my Agon virtual system you can read about, its name Essential 3150/3160 and exist 7 gentlemans over the audio world that till today are way proudly owners.

Which were the main targets when we started that way learning project?: accuracy ( not analytical but accurated. ) and high resolution putting the overall distortions /colorations/noises and the like at minimum and fortunatelly and after hundreds ( literally. ) of tests active and passive parts, modeling boards layouts, measurements, listened long sessions of recordings where we know even the kind of " color " of its " errors " and the sound of the tick and pops, listened evaluations against other phonolinepreamps ( integrated or separated. ) like: FM Acoustics, Gryphon, Dartzeel, Boulder, Lamm, Audio Note, M.Levinson, Krell, Halcro and others ( this similar products came some from my friends and some from my dealer friends.
When we finished ( after 3 long years for the 3150 and another year for the 3160. ) we was and are totally sure not only by our " mouth " but from my audio friends that nothing ( and I mean it. ) can’t touch our Essential.
Even today is way competitive against any other unit you can name it.
For the same targets a couple years ago I finished a self design and manufacture ( along other friend. ) a unique tonearm.

I write this not because I’m a conceit person no nothing like that, far away from there.

You can read in my Agon virtual system, please read it carefully, why the system has that so high resolution with no place to hide anything.

Anyway, I will test the ODAM and will see if can beats the WIMA because the boutique caps that I tested in my system no one outperforms the WIMA in the speaker crossovers.

""" Wima caps are not top class in resolution or refinement. """

I respect your opinion but IMHO no other cap has the WIMA " perfect " resolution and about " refinement almost every audiophile has his own definition.

Now, things could be the other way around: that with out very high resolution room/system we can’t be aware of the greatness of WIMA MKP10 because is an uncolored device with no self signature: just straigth with no common audiophile adjectives to describe the sound quality.

As any one here my reference is live MUSIC and in my case: seated at near field position like the recording microphones positions: nearfield.
My main room/system target is to stay truer to the recording nearest to it.

Rigth now WIMA gave and gives me a nearest place that ever before to that target.

I’m not married with anything but MUSIC and I’m a really a severe critic of my system and try to be very objective about and over tests and evaluations/comparisons too. You can be sure that I don’t like mislead my self.

I would like to know where you made the ODAM comparison against the MKP10 or other caps against WIMA.

Your statement: """ Wima caps are not top class in resolution or refinement . """

was exactly my way of thinking several years ago and that’s why I have in " stock " some values of WIMA caps, many because everywhere where I seen Wima I changed for other " better " cap.

I will finish the overall speaker caps changes and after that maybe I will do the same ( step by step. ) in my electronics.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

JFYI
A diyaudio member did some interesting ESR tests:
https://www.diyaudio.com/forums/parts/346861-esr-measurements-capacitors.html