Rip it out and replace with 5 1/4" primed white and then caulk the gaps, fill the nail holes and apply two coats acrylic paint in satin sheen or semi.

I agree, dont try to make what you have, something it isnt. Just remove them, and buy new preprimed that you really like.

Home Depot pine primed colonial looking baseboard runs $15.50 for 8 ft. Shoe about $3 for 8 ft. We bought 15 ft lengths for walls - less scarf joints. They also have Alexandria pine primed moulding that looks like it already has a shoe on the bottom. *Wish I'd seen this a couple of years ago. You Tube removal of old baseboard so you don't put holes in your drywall. Use nail gun with a compressor to attach new moulding. A power mitre or miter saw for the corners and scarf joints. Not difficult if I can do it, depends on your DIY skills - that's why I pointed out the pinterest methods.