Sounds to me like, in the words of my departed FiL, the bike doesn't owe you any money. You've had 5 years use out of it and done some riding on it in that time. It doesn't sound as if there's anything on it that you want to keep, so swapping parts off isn't going to have any real value.
I agree trying it with the new stem would be worthwhile, you've bought it, you might just as well give it a go, it might change things more than you realise. Presuming that does you no favours, decide what it's worth to you (factoring in the extra space of not having it around) and try and sell it on. Chuck the stem in your parts bin for some time in the future, sell it separately or add it in to the bike sale to get rid of it.
If the bike is of no use to you then having it sitting around is just a possible trigger to get grumpy.