I'm with everyone else, I like variety. And I know that's going to be an issue when I start kegging because I'm going to want a minimum of 5 taps going at once. Probably more.
As far as your question goes... I did start with the same kit for both my second and third batches... but I didn't stick with the kit. I have a hard time with things like that. My first kit was a Brewers Best kit, Chocolate Milk Stout. It was ok. I followed the instructions. Second kit was from Northern Brewer, Dry Irish Stout. Not being able to leave well enough alone, I added a pound of kiln coffee malt to the steep and a bit of DME to the brew. Turned out ok, but I later discovered that it benefited greatly from aging, one year in the bottle made it perfect. Third kit was a NB Dry Irish Stout. I added some DME and Lactose to it to make it a sweet stout. Fourth kit was a BB English Brown Ale that I added to. After that? I forged out on my own and started playing with partial mashes and my own recipes. Brewed a couple other modified kits here and there but, like I said, I can't leave things alone.
That said, I don't recommend that everyone follow my path. You need to be comfortable with the process before moving on and there are a lot of good kits out there. If you want to try partial mashing, get a grain bag or paint strainer bag, get a pound or two of say, pale 2-row malt, and combine it with the steeping grains from a kit. Read up on BIAB brewing, because that's what you do with a partial mash. Gets your feet wet so to speak without doing a double back flip off the high board with no experience.