Good question.
I started with a $50 plastic tripod, then a $200 combo, Manfrotto and Bogen kit. Then my third (and final) is a Gitzo and RRS kit. I personal like the Gitzo but it cost a lot more than my previous tripod. I still use both, and just last weekend, my older tripod was used in a pinch when my friend didn't bring his.
As for regrets. The only thing I would say is it's a big investment but I figured things like tripod rarely change. I knew from using my older tripods for years what I wanted and saved up, plus I use my tripod about 50% of my shooting so it's getting used, but not as often as I like with the current weather. 
I would recommend if you're unsure about buying a high end tripod (anything above $500), first stop by a local photo shop or photo meetup, and look at the various styles. See what gets you for X amount, then what gets you X+$100, X+$200, and so on. Then decide what features you really need, and how much they cost.
Once you figure out that you need carbon fiber legs, but not a center column, you can budget out and start to search for the ideal tripod. Buying used is a great idea, or buying a good name brand, as you can sell it down the line for less of a price loss.
While I like my Gitzo, I wouldn't recommend everyone buy one. They are expensive and not worth while if you don't spend the time using a tripod.
Good luck!