Phono preamp worth it with MM cartridges?

If you have a friendly dealer take the $2k and your P3, and exchange for a P6 with the Ania MC + Sutherland KC Vibe phonostage. THAT will be a very noticeable upgrade to your record collection.

@chakster, "todays MM cartridges are 95% junk." 

That is quite some generalization chakster. Do you have any additional references on that? Granted, the cheapest of the cheap cartridges are moving magnet cartridges but I do not think any of us take a $15.00 cartridge serious. 
Since you think MM cartridges are superior to MC cartridges does that make 99% of them junk? 

I share the general disrespect for the Exact, but defend the MM pre in the Elex-R.  What you want is a better cartridge, perhaps a Benz Ace HO?  Boron cantilever line contact nude stone, for under a grand. Another good one is a Hana SH.  And order a set of AS shims. 

Roger,
a good phono stage makes an improvement with either a MM or LOMC cart.

There are quite a few good ones out there, just depends on how deep you want to go into the woods. In the sub 2k range look for a used Manley Chinook. Does very well with both MC and MM carts. Have owned two of them over the years, you can pick one up used for 1400 to 1700 range.
The latest model has a switcher power supply so would avoid that, all the earlier models have a big fat toroid in the power supply section, which is what you want.  

I have personal experience with the elex-r built in phonostage as well as a rega p2 with the exact. The exact in all honesty had more "attack" than when I moved up to my Clearaudio Concept Wood table and the entry level Concept MM cartridge. I will go ahead and call the concept MM cartridge junk. Detail was improved, but everything else it offered was a step backwards. I accidentally broke the cantilever after too many drinks one night, which lead me to the sub $500 Hana EH which is a high output MC cartridge and I could not be happier.

Also, the Elex-r phonostage isn’t great, but it is decent. I moved to the Musical Surroundings Nova III and this phonostage is superb. I almost went Lehmann Black Cube but no local dealers stocked it. Michael Yee and Musical Surroundings have phonemal phonostages and even offer the option to add a liner power supply. This added even more "Identity" to the phono. I can highly recommend even calling Musical Surroundings as they have someone named Ken (I believe?) That you can talk to and won’t BS you into buying their products.

All in all, get rid of the exact, avoid the entry level Clearaudio MM and pick up either the Phenomena or the Nova III and don’t look back. That’s what I did.