Like you, most of my portraits have been 'practice' paintings from celebrity photographs. It seems as though those are the highest quality photos we can find to work from. At this point for me, however, I have sworn off celebrity portraits til one of them is willing to pay me for it
I think paintings of 'real people' have a bit more 'bite' as far as landing commissions. When I finally got away from the celebs and painted my daughter, many friends and family loved it and it landed me 2 commissions, something I never got from Clint, Elvis or any other celeb portrait I did.
I think when youre starting out, learning to paint and searching for subject matter, its alot easier to spend the time working on famous people. Everyone knows what they look like and can form a judgement based on that. I also think that you learn something new with every portrait you paint, at least I do.
From looking at your web site, I'd say youre ready to start working on portraits of common folks, as Cynthia has suggested. I thought about throwing up my John Lennon portrait here too, but I wont bother. You can visit my web site to see all my glorious junk. (on a side note - at my web site, I have all my portraits lobbed into one page. By the end of the year I'll have 3 or 4 more portraits to add, at which point I'll separate all the celebrity portraits from the 'real people' portraits and perhaps eventually eliminate the celebs altogether.)