So I have an Ibanez RG prestige for $700 with EMGs, but I don't like the floyd rose-style system (its a pain in the ass to tune, and I haven't restrung it in 6 months because it's annoying), the pickups pop up every couple months, and from doing absolutely NOTHING, the tone knob broke. Anyway, I'm thinking of trading it in for an SG special, because I like Tony Iommi. I'm only spending $750 at absolute max. As the title says, I play metal. Also, do you think that I should get a new guitar, or just keep my old one. I've been playing for a few years, but I'm by no means an expert guitarist.
If you like the SG, you can get the SG. Whatever guitar you own will require periodic maintenance and repair. An SG is no different.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
Odd your having quality issues with a Prestige as they are typically excellent built guitars.

With the right amp and pickups you can surely use an SG for playing metal.
"A well-wound coil is a well-wound coil regardless if it's wound with professional equipment, or if somebody's great-grandmother winds it to an old French recipe with Napoleon's modified coffee grinder and chops off the wire after a mile with an antique guillotine!"
- Bill Lawrence

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An SG is an excellent guitar for metal. I bought my SG 12 years ago and just love it. Am not a metal player, but play some hard rock, grunge etc. Trust me, it's a guitar that can really let rip. I think the Special comes with Gibson P94 pickups rather than Humbuckers - wonder if you'd be better with a Standard if you're only gonna play metal. Nothing roars like a humbucker.
Some of the SGs are avail with compound radius necks, most i think are 12" but there are some old 10" around too i think

I'd probably stick with the prestige though, change the strings, one at a time it's actually as fast as a hard tail, learn set the FR up right and keep it right or i hate when people do this, but block it if you can't master it, also knobs don't break from nothing