I can back this idea, though some portions need tweaking IMO.
Solar Flare Visor is somewhat OP for my tastes, but then I remember Solar Flare Armor by default works like a Tabi. If that Tabi effect is removed and replaced instead with the ground stomp I can see some use for it.
Siphon Buff on Nebula hat is a bit too OP. Maybe you can have it deal 30 damage per 150 Mana regained to limit abuse of extended Last Prisms.
150 Mana gives you two additional seconds of focused Last Prisms, and 375 HP (500HP -25%) on 10 damage gives you 37 restores. 37 * 2 = ~74 seconds of focused Last Prism fire without any damage debuffs gained. My proposal gives you only 12 restores from a full 500 HP, equaling to an approximate 24 seconds of uninterrupted fire.
How does the Stardust Hood behave with regards to Stardust Dragons?
The Vortex Headphones seem to lean more on shot speed. Might make the SDMG a bit more OPier, but if this also works for bows then why not. Do note that this reduces a sniper rifle's use time from 35 to 23~, and adds autofire. Given some crit bonuses, this might make the damned thing more OP than ever.
The Eraser is a nice idea. I take it they disappear at the same rate as they infect other blocks? The Eraser needs another counterpart though; one that encourages biome growth, at faster the rate than they did pre-plantera.
The Moongold bag is awesome; though stat caps need to be placed as it would end up making you deal piddly squat damage after using the 20th bag. Or maybe have a powerful boss even stronger than the Moon Lord, that starts exceedingly strong but becomes marginally weaker per Moongold bag used, and ends up resetting the stat boosts of both beacons and Moongold bags?
Of course, getting this reset item should be difficult. Not sure if you should paygate this a bit too much, slot machine it, or both.