Tried to replace the dash speakers on a Gen5 Camry and cannot find a 3 1/2" replacement. They are all too large. The stock speaker looks to be a special size.
HOWEVER, I had a pair of LPG 26NA tweeters and fashioned a mount for these out of 1/4" hardboard. With a simple first-order crossover and properly padded down, it sounds great even with the stock 6x9 midwoofer in the front door. The problem with the lack of clear treble in the factory system is with the poor dash speakers. The front 6x9s are actually pretty decent quality, though I did add some damping material behind to absorb the back wave (which clears up the midrange a bit).
Now after replacing the HU (more power -- the low end Sonys work well and look nice in the Gen5 Camry), my next step is to try a pair of 6.5" Vifa midwoofers in the front doors.
Wife thinks I am crazy with all this tweaking, but it looks promising.