I'm a DIYer so teke this advoce with that in mind!

With the grille in the lower part of the fireplace insert, I don't think you can build up the hearth (one layer of tile on it probably okay, creating a "raised hearth" not a good idea). Since that looks like an insert to me, bet the white mantle would pull right off. Then you could tile up at least halfway and put in a new mantle (white/traditional or reclaimed/barnwood look or whatever you want).