I'm eagerly awaiting some proper reviews of the new MK 950 speakers and attempting to track some down locally so that I can hear them for myself. Tom Andry has put in a request to Gene to see if they can score a 950 set for review, so let's hope that pans out!
In regards to getting the most improvement for your money, I will also strongly support the suggestions that you acoustically treat your room. You are correct that new speakers will make a bigger difference than any other
equipment upgrade. But new (and better) room acoustics will make a bigger difference than new speakers!
Take advantage of
Auralex' FREE Room Analysis. It costs nothing but a few hours of your time, so it is WELL worth the effort!
GiK Acoustics and Auralex are both fabulous companies that sell very affordable room treatment products and a whole-heartedly recommend both companies.
The new tweeters in the 950 series supposedly do have higher power handling. If your 750 speakers are having difficulty at very high output levels, then there is a decent chance that the 950 series will offer an improvement in that area. But I am only saying that based upon information that I have read. I have not heard the 950 speakers nor seen any measurements, so I would certainly not recommend them only based on that!
Treat your room. That really should be your primary focus. Personally, I'm not a fan of EQ'ing speakers because it is rare that people or programs measure with fine enough gradation to properly adjust higher frequency output. Use active EQ for subwoofers for sure, but not so much for speakers unless you are limiting the EQ to the lower frequencies of the speaker. I've toyed with the various AutoEQ systems (Audyssey, YPAO, MCACC, etc.) to no end and I've never come across an instance where they didn't reduce detail. So I don't trust active EQ for higher frequencies, but room treatments can genuinely improve your room's acoustics, which DOES help a great deal!
If you are a fan of M&K's sound, I would also recommend that you consider Emotiva's speakers as they have a very similar design philosophy, but are less of a rip-off than the cheap parts at high prices used in MK Sound's speakers and subs..