I wouldn't add any more plants or foliage to the front. If looks fine when everything is leafed out. I think the turn off for buyers would be any abundance of shrubs that require high maintenance like regular pruning to keep them from overpowering the house. I'd suggest removing the lopsided tree by the chimney. I'm more of a fan of loose foundation plantings, but I think your house looks marketable with just a bit of simplifying and sprucing - have you power washed the brick porch and walkway?