Add a strip of trim a bit above already existing baseboards, paint between, and you get faux thick baseboards! Other good ideas here as well. 31 Easy DIY Upgrades That Will Make Your Home Look More Expensive
*add this to build up baseboards in house - To make your baseboard more dramatic, add small pieces of trim to the top of existing baseboard, add a few inches and add another piece of moulding. Paint the wall and trim white.