Even if it doesn't increase the merchandise profit, It'd be really fun to see where it all comes from. The more options in the game, the more fun. That's another reason GLB is SO popular. They have SO many options that it took me 3 days to get through it all.
What would be cool would be to design the Jersey's, T-Shirt's, etc. Add your logo to it. etc. Then to add more accesories and products, make it cost $10k to implement a new product or something? I dont know, just an add on.