Is it really that weird that Luke's lightsaber have been found though? I mean it dropped into what was basically just a gigantic air vent in Cloud City, I'm sure there would be something, or someone to collect all the trash that might get dropped into it, that just makes sense. And we've already seen the ugnaughts rummaging through scrap from the city, so I don't see why one of them would pick up the lightsaber. I actually would find it weirder if the lightsaber weren't found by anyone. Plus a lightsaber is a pretty unique and valuable item (espeiclaly during the time of ESB) so it makes sense that some greedy little ugnaught would have picked it up. Being such a rare item, not to mention an illegal item under Imperial rule it makes sense that it would have changed through a lot of hands. And we already know that someone (most likely Kylo Ren) picked up Vader's charred helmet from Endor, which is also kind of weird, but far from impossible or improbable. After such a big and significant battle someone would have gone through the ruins, and Vader's helmet would also be quite a valuable item. It would be like finding Hitler's skull in the bunker or something similar.
I agree that it's a bit weird that both of these items seemingly has such an importance to the plot, but hopefully they will have an interesting explanation for Kylo Ren's interest in them. Plus it's only the first movie in the trilogy and it could turn out to be a somewhat clever way to tie the OT with the new films, and hopefully they'll be gone in the next two films. This seems the most likely since Abrams has talked about treating TFA as the link between the two trilogies and the transfer into a new story-line with new characters.
Could the lightsaber itself have some connection to the force perhaps? Considering that the film is called "the force awakens" and that there's been rumours about about the nature of the force suddenly changing, scaring Luke into exile, etc. And then there's the whole thing about Kanata showing visions through the lightsaber. Could the lightsaber and Vader's helmet be important through their connections to force users? Everyone assumes that kylo Ren is just a Vader wannabe, but maybe he (and perhaps the "Uber" character) actually have a practical purpose for them, like a ritual or something? Could the items themselves have a certain power to them. The EU has definitely played with these "occult" like aspects of the Sith and if Kanata can extract visions from an item then that could be what they're going for in this film. If that picture of Kylo Ren in the snow really is outside a sith temple, then a ritual of some kind could definitely be part of the plot.