Modifying or selling and buying new?

I'm having some trouble making a decision here. Lately I've been growing a bit dissatisfied with the performance of my Les Paul. Yes, it's a good guitar for beginners, but it does have some issues that bug me, so I've decided to either modify it or sell it and my Power Strat (a cheap beginner guitar with pretty much the same issues), and buy a new guitar to replace it next month. The part that is giving me trouble in making this decision is that I could make the LP better suited for my style by just switching pickups. But doing so would cost at least 2/3 of the guitar's value, which I think is a bit too much, when the over-all quality of the guitar doesn't improve much by doing that.

If I were to sell it, I believe I should be able to get at least 200$, if not more, which would go a long way towards helping me afford a higher-quality guitar, like my SG, ES or Martin. I know what I want from my dream-LP: Rosewood Fretboard, non-bolted neck, Mahogany body, Alnico Pickups (I've looked at a few, and Seymour Duncan JB or DiMarzio Tone Zone (I think that's the name) seem like a good choice for my style (70-80's-style Hard Rock and Metal)). That's all I know I want. My current LP does deliver most of this. It just drops out of tune once in a while, and can't get close enough to the 70-80's tone I need.

I just can't decide whether to actually sell it or not, though. Anyone got any recommendations? It's not that it's a bad guitar. I just think it has some issues that will be expensive to fix. So would it be best to modify it to fit my needs? Or will it be better to sell it to someone and then buy a better guitar?