The only problem with weapons is then getting the "better" weapons would require doing an achievement. And that is kind of BS. Yes, achievements are optional, but the intent for my suggestion was that players would get an item/look that has ZERO effect on anything else. It would just be a collection deal.
It doesn't have to be a "better" weapon. Perhaps a different weapon, like a sniper with thermal ocular, the scorpion or a weapon that bring a difference in gameplay (like the turian's sniper gun). After all, here are some bonus you gain in ME1 :
Finish the game twice : weapons deals 5% more damage.
Finish the hardcore mode : unlock new difficulty mode.
Kill 150 enemies with pistol : one skill gain 25% duration.
Finish the majority of the sidequests : 5% exp bonus.
Taking a lot of damage during a run : 10% bonus on the shields.
...
Not really game-breaking bonus, no? If you don't want it, just switch them off with a cheat menu in MEA.
Edit : Changed the topics main title. Sorry, my english is poor...