Yes and no.
I can do basic stuff myself: slimming shirts, slimming trou (without having to redo hem), sleeves.
And now that my closet is filled out, I can be more choosy. But even then, I would def. not pass up a choice piece (Kiton, Attolini, etc.) that filled a need in my wardrobe based on $50 worth of tailoring. Remember how much these things cost retail, and $50 in tailoring is a no brainer.
I 100% don't regret most of the tailoring I've done, since I got great use out of those items and was then able to trade/sell them up down the line. You just need to take that cost into your analysis.
Edit: Think of it this way: Add up the purchase price plus the alterations/repair cost, and ask yourself "Would I pay that total amount for this item if it fit perfectly?" If yes, do it and don't regret it. If not, then try to find someone it works for (and try to give them a good deal on it).