first things first.
1) Every MMO has botters. This isn't just MMORPGs. COD, Halo, LoL, HoN, BC, FFXI, WoW, PWI, Atlantica, RoM and FFXIV ALL have botters. You aren't going to stop botters. No one will. SE TRIED to stop them, but in return, they lost most of their player base because of their anti RMT actions.
2) There isn't a limit to how many items players can get in an area. I'm not sure where you got that info from, but it's wrong. You get gathering fatigue. It's like...every 150 or so items, you start failing all gathers. This isn't because of botters at all. It's because of SE trying to stop botters, but they just go right through it because they still get SP for fails.
3) Botters aren't killing the economy. Those that are killing the economy are the greedy players that try to outdo the bots. "Ok, so this botter is selling his item for 50k, well I'll sell mine for 40k haha! take that you bot!" Do you know what's going to happen? He's going to lower his item by even more because he can afford the loss. Say he brings his down to 30k. Well, you can't compete with that because if you sell at 30k, you'll be at a loss with gil, but the botter can make them faster and cheaper so taking a 20k loss is not a big deal to them while you are sitting there with your 40k item, unsold, because you decided to be stupid. If a botter is selling an item for 50k, sell yours for 50k or only like 50gil cheaper because bots will ALWAYS outdo your price if it's substantially lower and they won't suffer for it at all.