There's nothing intrinsically wrong with a mid 60s Guild, it's more of a question of what sound are you looking for. If you're trying to get something sparkling and crisp, you're probably looking at a Strat, Tele or Gretsch. Want to sound like the Byrds? You need a Rickenbacker.
Which guitar do you have (guessing a Starfire of some sort?) Does it have the humbuckers, P90s, DeArmonds? Each has a distinctive tone. I love old Guilds, having a 74 S100 and and DeArmond Starfire myself. They have a unique sound, not like an SG or 335.
You can always change the pickups, just keep the old ones so that you can restore it if you ever want to sell it. With a standard PAF, a Starfire 4 sounds really close to a 335 in tone. Plus, remember that an amp (or emulation) can totally change what your guitar sounds like. Depending on how discriminating your ear is, an Epiphone with the same pickups as a Custom Shop R9 will sound pretty darn close. The differences are more in feel, and other intangibles.
Old Guilds in good condition can fetch a pretty penny. Just check on Reverb.com. Don't let it go for a song just to buy a $500 Mexican Strat!!!!
I have the Starfire III. The white pickups back then.. single coil... you note different sounds... but i'm wondering if once its processed on its way to cubase (via UR12), if the sound is degraded or changed.. (as far as i can tell, the sound out my amp and out of computer is similar).
But as you mention... if i start bastardizing the sound with plug-ins, such as amp simulators, maybe how the electric sounds is not that big a deal.. The sound i want can be messaged by post-processing.
about my Guild (which maybe i should keep, lol)
**** SNOOZE ALERT.. DO NOT USE HEAVY MACHINERY OR DRIVE A VEHICLE WHEN READING THE FOLLOWING
When i joined a band in 1970, I had no idea this guitar would be of value. I bought in i think '65 for like $350.
1) I lent my guitar to my lead guitarist for about a week. Back in the day, we guys wore these 10 lb 6" diameter (slight exaggeration) belt buckles.
I had worn off a little of the finish at the back, but when i got it back its like 1/4 of the back was down to bare wood...
Lesson: do not lend your valuable stuff out.
2) There was a time where many people bought these ENGRAVERS to protect their stuff. I engraved my SIN on the back (that was before the age of Identity Theft)...
so year later i had to scratch out some of the numbers.
3) I applied lettering to the wrist guard (my band's name). I removed most of it, but some of the stuff is still there.
4) I lent my guitar to my daughter's husband who wanted to use it in a photo shoot. They DROPPED the guitar and the neck separated. They put in a steel rod
or something. I am sure that just dropped the price by a grand.
Lesson: do not be stupid enough to lend your valuable stuff out A SECOND FRIGGIN TIME.
(good point on not selling it to buy a cheap one.