Upgrade From SME IV to V - Worth It

It depends initially on the period of origin of the IV, initially the V had Abec 5 bearings while the IV had Abec 3 then over time they made improvements to the entire V IV and 309 series.
I would keep the IV replacing only the original wiring with pure silver and investing the money saved in an upgrade of the head or phono.

the V has some more features as standard (silicone damping tank not necessary because if badly adjusted it suffocates the sound) possibility of VTA on the fly, lower tolerances than the IV but not to be heard obvious differences that do not let you sleep at night, VDH cable in silver; according to several enthusiasts who have had the V it seems to sound more  soft compared to the IV but these are nuances.
Changing the head for the better you notice more differences than going from the Sme IV to the V

Many thanks for everyone's input/advice. The general consensus of opinion is; keep the SME IV. Good advice, which I plan to take. The suggestion to replace my Clearaudio Maestro V2 Ebony MM cartridge with a Soundsmith Voice MI cartridge is interesting, will follow up on this.

I recently purchased the Analouge Productions UHQR The Doors LA Woman disc. I honestly don’t know how a 53 year old recording can sound this good on a 33 1/3 vinyl disc, simply mind blowing! Surface noise was non existent, dynamic range was outstanding as was frequency response. Overall, the best vinyl pressing I have ever heard. Also worth mentioning, packaging and associated printed material for the new disc is simply outstanding, as good as it gets IMHO

I recently purchased the Analouge Productions UHQR The Doors LA Woman disc. I honestly don’t know how a 53 year old recording can sound this good on a 33 1/3 vinyl disc, simply mind blowing!

no, it's not amazing, it's analog and that means investing in the components that make up the turntable is very important.
Even on vinyl records from specialized audiophile houses dating back to the 70s, listening to them today you are surprised at how good they sound.
Vinyl has everything you need, the enthusiast just needs to be able to find the way to extract everything that is inside the grooves.
It's a shame that current commercial or audiophile vinyl pressings have reached unaffordable prices.

It is easy to keep the IV, I am keeping mine, at present there is no intention to reintroduce it, but that can always change in the future.

As the owned IV is a Donor Arm to be used, 'when it eventually happens', on a DD TT with a Plinth Design to have Three TA's mounted, ( 1 @ 9" - 1 @ 12" - 1 @ Variable P to S dimensions ). The idea that comes and goes, could be put in place  to show visitors to the Home System the differences between TA's on a TT that can mount Two TA's.

The present plan for the TA, is to watch how the value appreciates as a used sale item. If the IV or V model is entered into the used market today, and the sale is carefully undertaken. The two models are almost on par for being accessible to funds as a ATM.

There is still good experiences to be had, if the footwork is put in to get out and experience alternate devices being used to enable a Cart' to function. One of these experiences may prove to have a profound effect and make the idea of change to  become a unavoidable. A decision may be forced to be made, where one option chosen is seemingly going to be much more advantageous.

Making a decision about the IV, that's how it went for myself anyways.     

Exchanging the VandenHul phono cable for a Graham unit will be an improvement. The IC 70 and especially the IC-90 cables from Graham really add like to the SME tonearms.