You'll get various opinions on refinishing. the best job is if you can take the thing out, it gets sandblasted to the ci, and then a new finish is applied. For the cost of that, you can often buy a new one. Doing it in place will yield lesser results. A liner is fraught with potential problems...the worst is where it leaks between the liner and the tub and it's like stepping into a waterbed.
There are probably some epoxy paints that might work, but the cost can be high, and you need the proper equipment to apply it. There are some pretty inexpensive tile out there that may end up looking better than trying to paint it.
SOrry to be so negative...it's tough to make a durable end result over the existing stuff. It can be done, but generally, it's not a DIY'er thing, or it will end up looking like it.