I agree with everyone. It is absolutely worthwhile -- even necessary! -- to buy some clothing items that fit the body you have now, and that make you happy. And yes, it is possible to change body type; for example, a woman who was an hourglass in her youth may find herself more of an apple in her menopausal years.
One thing nobody has asked yet: do you plan to try to lose the weight you have gained? You say you have been neglecting fitness for a while, but assuming you try to get back into shape, is it likely that you will go back to the size you were before? If so, don't toss out the clothes you like that are too tight.
The reason I say this is that I gained a helluva lot of weight in both my pregnancies, and both times, and wasn't sure how it would affect my future figure. I was prepared for a permanently different, and possibly bigger, shape. The first time, I did lose all the weight, and was able to fit back into every last pair of pre-pregnancy jeans -- but not for a whole year. That meant 12 months of a gradually shrinking figure, which of course meant purchasing clothing (bottoms, mostly) in gradually diminishing sizes. The second time, I had less time to exercise (two kids and a mortgage will do that to ya), so I never did get all the way back down; I'm still a size bigger. Two years after my second child was born, I finally did a massive closet purge and got rid of all of those prepregnancy clothes that still don't fit me. And let's face it, if I ever do beat those last five pounds off my body, my prepregnancy clothes will be so woefully out of style that I wouldn't wear them anyway!
My point is, if there is a chance that, in the next two years, you will get back down to your original size, it's worth keeping your old clothes. Treat it like a pregnancy: your normal wardrobe is temporarily "on hold," but you must buy some nice things in the meantime so you can look and feel good about yourself.
