During my time owning the 60D, I mostly shot landscape/sunset and night street photography. I also will be assisting my sister in shooting a Wedding as well, it will be a nice to get my feet wet into wedding photography.
60D is just fine for those purposes, though obviously for night stuff a 5dii/6d would be nicer. But, as you can see right away, its hard to find cheap glass for full-frame, so, you'll spend $1500 on the body and another few thousand on lenses. Adds up fast.
The amount that I want to spend is tentatively $2000, but I could see myself selling the Tamron, and forking up a little bit more to get a 6D w/ 24-105mm f/4 IS, but then again, I don't know if I could justify the price for essentially a "first-time" DSLR.
Well, a 60D is pretty dirt cheap at this point, seen them in the $5-600 range fairly frequently. So, that leaves you $1500 for glass. If you do a lot of travel, the 15-85 would combo nicely with that as your kit lens. And then a few primes (85mm/100mm and probably something wider, maybe 24 or 28mm) and you'd have a decently well rounded kit. The primes would work for street/night photography, 15-85 gives you some landscape flexibility. And for weddings you'd be covered indoors and outdoors for assisting.
And if you eventually decide to go full-frame, all the primes would still work. And the 15-85 holds its value fairly well.