Would be an interesting move if it comes to fruition.
Could potentially help solve a few problems. Valencia was excellent last season and one of our most reliable and consistent performers at RB, however he is getting on in terms of age and when he loses his dynamism and physicality (hopefully not any time soon, as he does seem to be pretty professional in his approach) he'd lose a major part of his game and I see him going down the road of a Zabaleta rather than Alves for instance. Hopefully he does maintain his physicality just as Zanetti and Cafu did for example but we can never truly know when his physical and overall decline would begin.
Secondly, it's no secret how at times we struggle to stretch play in the final third, lack that consistent flair forward (Sanchez, Hazard, De Bruyne etc) who's capable of providing that constant threat or match winning brilliance, nor do we have the creative genius of a David Silva or Eriksen who can unlock defenses. Hopefully Rashford or Martial or Mkhitaryan can make that step up though.
Our wide forwards - Martial, Mata, Mkhitaryan, Lingard and Rashford - are precisely just that and love cutting inwards and prefer central areas. We do lack some proper wing threat or ability to stretch play in the final third. Now Valencia as a RW does appeal to me in that he could potentially open up space down the other flank for one of our wide forwards and Pogba/Herrera whilst serving to open up the field and create spaces with his dynamic wing play. Esp with Aurier in tow (do recall Rafael and Valencia being a decent pair or could be imagining it).
Naturally, I wouldn't expect great service akin to Beckham or Alves for that matter, but his wing play and runs down the flank could alleviate some burden from our forwards, provide better balance as opposed to two forwards 'just' looking to cut in and provide our forwards and midfielders with a better platform to work with. Could potentially be worth a shot, esp given our array of forwards.