Buying, Developing & Selling On. . . . a good way to go?

Being the laziest designer in the world im always looking for quick ways to make money, whenever i see a really nice design being sold for cheap i always think it would be a great idea to buy it, make a few improvements, code it up with a few sub-pages and sell it on for like twice price or more. . . . i finally decieded to give this a try today and bought a nifty hosting design (PSD only) for $100 im going to develop it and try to sell it on for a profit, now the reason i ask if this is such a good idea is because it wont be my work, the main reason i design atm is not really to make money (as i dont make that much) but to try to improve everytime i make something new. If im doing this however i wont be improving but i will be making easier money so its kinda catch 22 for me

so do you think i should keep on like this or try to sell only my own work? or maybe try to do a little of both?