There are several issues that ranged combat has that tends to make it less effective than a melee build of the same investment. I think trying to fix all that from the weapons end of things is difficult and has the potential for abuse, which I why I started by modifying the base rules and feats for ranged combat first.
IMHO, a +1 bump in damage should not be a mediocre feat, it is a BAD feat. It is mathmatically weak and mechanically uninteresting; a mediocre feat can be either powerful or interesting, and a good feat would be both.
That was why I suggested adding additional combat options to the greatbow, to make up for the fact that it was more difficult to master.
Another possibility is to design a selection of payload-style arrows that could fire things like nets, tripwires, glue/acid/fire bombs, grappling hooks, etc, but these larger, specialized arrows would require a different kind of bow (exotic).
Balacing everything while still having interesting and unique weapons might be very problematic; I would prefer to restrict weapon selection to class, rather than by race, and just give melee-heavy classes more feats.
Good idea, but the mechanic of that would be very clunky, I think. There is an armor enchantment on the SRD called Fortification that reduces the chance to deal critical damage. I would either use that, or have it grant the bonus to your AC against rolls to confirm critical hits.-I think reinforced plate armor maybe should give some protection against critical hits and stay +8. Like decrease attackers critical range by 1 or 2.