Hypothetical:
1. Lets say power curve is 2.5 times base as the max (ex: 100 pt base damage will max at 250 pts). Lets say you can only get up to a third of that from crafting (ex: 100 pt base damage will max at 150 pts from resources), the other pts can be gained from other areas of the game (support skills/gear, character personal improvement web, being "in the zone"-activities in game) so that no one area will outweigh another and you won't have to max everything to get to max. The quality of the resource dictates the pt increase of the modification (ex: low quality-base pts; mid quality-10 pts, high quality-20 pts, very high-30 pts, epic-40 pts, legendary-50 pts). Gear itself has a quality based on the resource quality it was crafted with, but that won't directly effect the stats. Gear quality would effect the # of stats that can be modified (ex: low quality-one stat, mid quality-2 stats; high quality-3 stats; etc)...but...for every 2 stats that are modified you have to pick a stat that it's base drops below the base by say 10-20% (ex: high quality shotgun - modify damage plus rate of fire after which you chose range for the lower stat then you modded magazine size. If range base was 50 meters, then it drops to 40-45 meters.).
2. Modifications wear out and have to be replaced/changed. Gear never wears out but has a repair cost. The quality of the modification and/or gear adjusts the wear out time - say 2 hours of playtime for low quality modification in low quality gear as a base. For each quality above low on either will add 15 minutes of time (ex: high quality gear and mid quality modification - or vice versa - would have 2 hours 45 minutes of time before the modification wears out and needs replacing). Wear and tear is calculated by performing activities in the game, not standing around chatting at the crafting station.