Did your grills fit back over the rears? I put in a set of Polk Audio's in the rear of mine, and the tweeters stick up too high. For now I'm just living with it, but it looks tacky without the grills.
I didn't really notice much, if any, sound gain with my speaker replacement. I was disappointed really. I gained a bit in the high frequency end, but other than that I can't tell any diff with any type of music. (And I THINK I have a fairly discerning ear) The speaker these cars came with have squat for low frequency reproduction, but do a pretty good job with mid and fair with the highs. I see alot of others over in the audio forum coming to the same conclusion too. Unless your going to add some big amps, it may not be worth the money and trouble to swap out. What say you who have switched the fronts? Any real gains?
Best thing I did was add a subwoofer as jbaj007 did. I used a self-powered 10" SAS Bazooka tube. Fills in real nice, although you can hear it better outside the car than inside. I need to open up the rear deck through the storage trays too.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)