The answer to your question is totally subjective. It's in the eye of the beholder and as others have stated, it depends on a lot of variables:
•how old is it?
•how rare is it?
•how complete is it?
•how readily available are replacement parts?
•are there compatible parts available that will significantly improve design and/or function?
The older an item is, the more rare it is, and the more complete it is, the more I'm likely to err on the side of being a preservationist because it's only original once. But if the item has a lot of missing or broken parts, I'll likely be more open to restoration but depending on the situation, I may opt to improve upon the original by incorporating newer or better parts because I'm not opposed to creating a frankenvac.
Case in point: A few years ago, I bought my G5 and while I paid what felt at the time like a good price for it, I ended up spending more than twice as much on replacement parts as I paid for the machine in the first place. It came to me with a handle back panel from a G4 so it was already not original and because I was shopping price, most of the parts I bought were fully compatible but were for other models. It needed a brush roll, so I got one for a Sentria because it was cheaper and arguably superior to the original. The outer bag was shot, so I managed to come up with an entire outer bag assembly for an Ultimate G, including emptor and fill tube, for less than the cost of a new outer bag and gained a few minor design improvements in the process. The light gray G3 cord was a matter of taking one for a third the normal retail price. It's functional and the light gray color ties in with the similarly colored emptor on the other side. What I ended up with doesn't look bad at all, kind of reminiscent of a Classic III color scheme, and functions at least as well as it did when new. It's also not a particularly rare machine, so no harm done. I use it and enjoy it the way it is.
