Get a steel plate. One of the best upgrades for me as far as getting exceptional crust.
I am now using a steel plate and it has given me better results, but it depends on what you're looking for. So far I haven't gotten a crispy
crust on on my steel plate, though a lot of factors go into that (oven temp/bake time, hydration, fermentation, etc.). Quarry tiles are a good place to start even if you eventually move on to steel, because the tiles are so cheap.
I really like the river rocks idea - quite clever.
As for my opinion on parbaking, I haven't done it since I started using a better baking surface (stone/steel), but I don't think it's the worst thing you can do to a pizza. Unfortunately it is easy to overbake while parbaking, which can easily ruin a pizza. However, I don't think I could distinguish between a pizza that had been parbaked and one that had not by flavor alone. I think the bigger difference will be in the texture and crumb of the crust.