This has probably been suggested hundreds of times already, but here is another one to add to the list.
How often are you trying to make ql200 implants and you have to go to every damned superior store on rubika to find the right clusters above ql 170? I for one am sick of running laps through bor, newland, newland desert, rome green, rome red and omni trade (as an omni) and still needing half of the clusters i'm after. The amount of times a superior store doesn't even have a higher than ql100 stocked is absurd. It's a superior store.
Now, I'm not suggesting superior stores should always stock above ql 170, but perhaps if it was more likely to. My idea is along the lines of this: Each shop stocks 2 ql's of every cluster (most of the time), so what if, in a superior store, one of those was always in the range of 100-150 and the other always in the range of 150-200. Better chance of finding what you want in the first two shops at least, or even getting everything first try; yet still not guaranteed, making it too easy. Keeping the same routine for lower stores, advanced could do 50-75 and 75-100, and basic <25 and 25-50. Frankly I don't care so much about those stores because anyone with the ability to make a couple million credits is likely to just go to the superior store for lower implants to guarantee the higher ql cluster needed. I just don't want to have to do 10 laps of the aforementioned stores to collect all the clusters I need.