In theory if you do a 1500' circuit, then you would be slightly wider on downwind, but the centreline would be in the same position relative to your wing as it would be at 1000'.
So because of that, the 45deg pt for turning base would also be further out than at 1000', so noone should be descending on anyone, as you are further out than the 1000' guys.
Does mean you don't end up behind a 152 or a Sportstar at 150kts though
BTW Lasior, perhaps if the aircraft on 1500' calls "High Downwind" instead of just downwind? Also, I was taught to overfly at 2000AGL, although my current school teaches 1500AGL overhead. I just make sure to brief my students that at busy regional CTAFs, if they hear Eastern/Sunstate/Rex anything, or something of a similar size, expect it to be at 1500' on downwind.