Trump should build the ballroom.
But I'll go further and say that it's the absolute height of TND-induced mental retardation for Democrats to oppose it.
If I was still my 2016 self and thought Orange Man Very Extremely Life-Endangeringly Bad, I'd want all his time to be spent on trivial surface-level concerns.
Build yourself a gorgeous new ballroom! Change anything at the White House that doesn't currently have gold plate to remedy that deficiency! We need more colossal monuments in and around DC! Hey, can you do something about this golf course that's in disrepair so close to our nation's centers of power, we've heard you're incredible at golf courses. Hey, America's 250th birthday is coming up, here's a boatload of money you can spend however you want on making A Salute to Fireworks or whatever, we're sure you'll do it great.
Trump likes decorating and golf course designing. It makes him happy, and more importantly, it keeps him busy. If I'd been of the professional advisory class I'd have advised Democrats to fawn over his capabilities in these arenas and try to use Donald's Special Interests to keep him away from anything more important. Give him all the funding for all his pet projects and compliment him for the results, even if they're not to your actual aesthetic preferences. Fight him all day long on the important stuff that isn't just "skin deep" but slather him with money and accolades when he wants to do something silly that affects no one. Eventually his presidency is corralled into a very specific sort of containment as he sees it's more fun and easy to just do this aesthetic stuff, why bother with the difficult work of implementing policy?
Instead, they block him from even getting started on these kinds of aesthetic, trivial projects, which puts his focus squarely where they do not want it. It's unfathomably retarded.