Does Restoring an Item Ruin its Value?

So I recently came into possession of a couple of items that need restoration, one of these is the considerably rare Talk N Action Gordon, I was wondering however, that if I were to fix these items and restore them to how they would have originally looked, would this affect the resale value? I plan on reselling some of them to start to make my own money and get a steady income by selling some for quite cheap prices, e.g TOMY Molly without tender for £3, let me know if it does affect the value or not, I would find the information very helpful!

If you want to make some money, buy the anniversary sets (i.e. the metallic James, Percy, Nia and Thomas).  They may worth a bit down the road.  

Replacing the old stickers on tenders with new ones won't affect the value.   if you restoring the engine by lets say spray paint, the value will go down significantly.  It really depends on what type of restoration you want to do.

I think the resale value would only really be affected by how well of a job is done in restoration. If it looks good or is restored to a better working condition, I don't see any reason why it's value would go down, or why people would be against it.

[Super]

Yes, it would definitely affect the value if you are talking about any painting and/or decals/stickers. It would never come out like the special stickers used and the manufacturing paint and colored plastic as it was new. If you are talking about repairing the workings like motor, gear replacement and re-wiring, I would say it would not affect the value as long as the repairs were done very well.

This all being said, if your plans are to sell, I think it would be very important to list the restorations and/or repairs so any potential buyers would know exactly what they were getting and judge for themselves what the value is. If you are planning to sell on a site like Ebay...using the Auction and starting at a reasonable price might be the best way to go and let the market dictate the value.

So I gather it would be in my best interest as to leave my Talk N Action Gordon's plastic in the way it is, but fix up the lining so it at least looks good, it doesn't need any new stickers which is a bonus, as for selling the items I'd be doing it for cheap regardless depending on the item so I'm not too bothered if the value is decimated on them, more on the items I own is my concerns

@LeyLandVictory2 So if I had a plarail Edward that was very beaten up, yellow in the face and damaged running board (in terms of paint) and I restored it, it would be worth less than what it would be priced if it was a brand new item but worth more than it was when it was ruined? Is that right?

Yea, I would say so given Edward is not that rare to a certain degree.  if I type plarail edward, there will be a lot of listings.  

If you don't have a lot of experiences in restoring trains, I suggest people to master their craft using worthless engines first.  I always use Thomas to test out ideas given how abundant thomas available in lots and stuff.