I owned an Aragon 4004 mk 2 about 20 years ago or so. I doubt you will find it to sound harsh in the high frequencies.
$450 seems like a pretty good price for that amp. I would hook it up and try it out. The main concern with older amps is the capacitors, as they tend to wear out and need to be replaced in about 15-40 years, depending mostly on amp design and amp usage. The hotter an amp runs (Class A bias), or the longer an amp may sit dormant, can shorten the life span of the capacitors.
You should be able to tell by listening to it. If you hear any thumps at turn on/off, or a static like discharging sound while playing, then the caps will probably need replaced. Any local tech should be able to do that for a couple hundred bucks, then you should be good for another couple decades.
If no annoying thumps or crackling sounds, then just relax and enjoy the music. That's a good amp, especially for $450.
Cheers,
John