Just found this, not sure if anyone else has posted/seen this:

http://www.reddit.com/r/Diablo/comments/109x5v/ptr_is_up/c6bn5dz

Key thing: Each MP level adds 25% MF, MP levels 1-3 add 10% exp each, 4-6 add 15% exp each, 7-9 add 20% exp each, and 10 adds 25%. The aggregate bonuses for +MF% and +exp% at MP 10 are therefore 250% and 160% respectively.
Edit: These are values in inferno and do break the 300% cap.

So those are pretty massive increases. To put it in perspective, let's say you are PL 30 and you run with no MF (let's say 20% bonus from Enchantress). That means you have 110 MF base and 185 MF with NV. Running on just MP3 (which has already been confirmed to be equal to current Act 3 difficulty) gives you 75% additional MF. This is equal to 25 Paragon levels. PL 30 to PL 55 is about 1.7 billion exp. At 20M/hour, you can have the same MF as a guy who has spent 85 more hours grinding exp just by increasing MP by 3. This becomes even more significant at higher PL levels.

For exp, going from MP0 to MP3 gives you the same bonus as a perfect Leoric's ring. At MP10? A perfect 30% Leoric's only gives you an increase of 11.5% exp.

So here are a few predictions I have:

1) MF gear value will drop rapidly. MF gear suffers from diminishing returns (since the percentages are added, not multiplied). For example, let's say the chance for a legendary to drop is 5%. With 500% MF, your chance is increased by 5x or 25%. Your chance for a legendary is now 30%. If you put on 100% MF gear, you have 600% MF. Your chance for a legendary now is only 35%. It's only about a 17% increased chance by adding 100% MF.
2) Leoric's Signet value will tank. Probably a no brainer, but with the additional options to increase EXP, diminishing returns on signet bonus, diminished value of PL MF, I can't see anyone using the Signet. Even the richest of the richest because it's probably better to just run MP10 and put a DPS ring on than to have a paltry 20% bonus.
3) I think Topaz might spike also because of the diminished value of paragon leveling for MF. Even though 31% is pretty small, I think people will be more interested in stacking MF now because of the ability to exceed the 300% cap almost immediately (PL 17 with zero MF and NV at MP10 already puts you at 301).

It's difficult to gauge the exact effects without actually testing the MP levels however. From what I've heard, the biggest difference is monster HP. If that's the case, then I think DPS gear is going to get even more expensive since the biggest barrier to farming efficiently will be the time it takes to whittle the monsters down.

Finally those Stone of Jordan investments will pay off...

I think only the high end MF gear might drop rapidly. People farming low-mid monster levels won't suffer as much from the MF diminishing returns, so it probably won't be quite as bad. On the other hand, if the high end gear drops in value, that'll have a cascading effect. I agree with your prediction, but I'm not sure if it's going to plummet fast.

I think Leoric's will tank hard like you said. If increasing monster level with a DPS ring gives you the same equivalent exp per hour, then it's really a no-brainer when you also factor in the increased MF.

@Khan Winning lotteries, making good investments, farming with efficient/offensive builds... I can only imagine how much gold/money you've acquired in the game ;-)

@sabin Ha! Not enough! I've had some losers. Like those emeralds until recently and those damn demon hand plans that didn't quite pan out. I'd also consider my investment in my CM/WW/EB build a bit of a loser since its not as effective as before. Maybe I'd consider it a "rental" since it was a good run while I had it.

No risk no reward, eh?