hell, considering the system being replaced and has been good enough until now, you could go dumpster diving every 5 years and upgrade his system for free, forever (or at least until people start disposing of computers in a more environmentally responsible way)
about 10 years ago i got a 1200mhz athlon, it was pretty sweet but within about 3 years it was no good for what I wanted to do with it anymore (was an avid gamer). ram standards changed meaning there wasnt much worth keeping (cpu slow, old style ram, mb didnt support newer processor) so it got turfed. thats a computer with over 10x the power of their current vet system thrown out as scrap. i would of happily given it to anyone who could make use of it. it's not a particularly uncommon scenario either
I would guess the vet is looking at it from an "if it works, dont mess with it" point of view, but from a geek point of view it screams "if anything goes wrong with that pc, you're fucked". good luck finding compatible replacement parts for even a 10 year old pc. remaining current is not just about chasing teh megahurtz. it's about being able to walk into a shop and buy a replacement for whatever component just let out the smoke