If you plan on reselling the I would leave them. I have two pipes with stingers, a Kaywoodie and a Dr. Graybow. Neither are what I would call great smokers. They don't smoke hot, but both pipes gurgle something terrible! I left them in just to keep the pipes in their original condition, but because of that they rarely get smoked.
I have an old Grabow that had a stinger. It was simply a push fit and after some wiggling and gentle pulling, it came out. I kept it, but I don't know why because I'll never sell the pipe and it's not worth much. To be honest, I've not noticed much difference with and without the stinger. The only advantage to having the stinger removed is that I can, if I wish, use a pipe cleaner during smoking when the stinger is out.
If they're permanently attatched, smoke them and see what you think. If you absolutely can't stand it, there are ways of removing them (albeit permanently) while leaving the threads needed to attatch the stem to the shank. My Kaywoodie smokes well with the stinger. Also, as with 4-hole 'Woodie stingers and some others, the presence or style of a stinger can be a sign of something unique about the pipe, particularly its age. Do some research, and maybe talk to a forum "expert" on the brand, then whatever seems like a good idea probably will be one.
My Mr. Brog has a stinger that I keep forgetting about until I go to clean it... One of these days, I need to do a comparative test with and without it to see if it makes any difference at all. It's a push fit, easy to remove, but once I do it will probably get lost.
I collect Kaywoodies, along with several other makes. The stingers do affect the draw a little and take a little more effort to clean. I don't really mind that. As a collector I want value for the money I put out, so condition matters. If the stinger has been compromised, the pipe is of no interest to me, simple as that.