It's not easy (or accurate or appropriate) to make blanket statements about certain model years or this place of manufacture over that place, etc. You could play three identical 1964 Fenders or three identical brand new MIA Fenders or three identical 2001 MIMs and find a pretty wide variance in feel, playability and sound.
People should also remember that the MIA Fenders are made just 30 miles north of the MIM Fenders. I read somewhere where a guy from Fender said the main difference between the MIAs and MIMs were that the MIAs were made by Mexican factory workers north of the border and MIMs were made by Mexican factory workers south of the border. This person said one of the main reasons the Mexi plant was built was due to regulations in the amount of spraying (paints, coats, chemical emissions) that could be done in SoCal.
(I know this isn't 100% true and some years/makes of MIMs have different hardware & electronics, different wood, etc.)
I just scored a '94 MIM P over the weekend. Got a good deal on it, with a good case thrown in. I played two other MIM Ps while shopping for a new bass. One was a 2004 which looked and sounded beautiful, but the owner said he had to tweak the neck every 2-3 months, so I passed. The other was a 2007 which I almost scored, but I ended up finding this '94 that just spoke to me. I know the conventional wisdom is that the earlier the MIM, the worse it is, but I really stumbled onto a winner. I played it through three rigs and it sounded great through each one. I don't even think I am going to replace the pickup, but I haven't decided.
This is my first MIM bass. I've owned many Squiers and Fenders over the years, including pre-CBS Fenders.
While in the store I also played a used MIA P bass (asking $999 for it) and a new MIA ($1399.)
I will not say the MIM is "as good" or "better" than the MIAs, but I will say I really liked the feel of the MIM. Maybe just because it is more broken in. The MIAs sounded a little brighter but then again the MIM may well have 20 year old strings on it. It does sound very good though. Very inviting warm thumpiness.
Can't say I wouldn't have taken an MIA over the MIM if I could have afforded it, but there honestly was nothing "better" in the MIAs or lacking in the MIM that made me think the MIAs were worth 3 or 4 times as much as the MIM.
Actually, one of the nicest Ps I ever played is one of those Classic 50s MIMs--it was honey blonde w/ gold anodized pickguard. Man, that thing was great, and the neck was to die for. I would love one of those. But anyway, I'm happy.
The only other MIM fenders I've owned were both Telecaster guitars. One was a late 90s, the other was (I think) a 2003. Both were nice. When I bought the later model I was actually planning on getting an MIA Telecaster but after A/B'ing the MIM with a couple of MIAs in the shop, I couldn't see a reason to try and justify spending nearly $1000 more.