FlyerTalk Evangelist
Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: BA Silver, TK E+, AA PP, Hyatt Globalist, Marriott LT Plat, Hilton Diamond
Posts: 13,053
Whenever I've checked, availability using Avios on Vueling tracks the lowest fare buckets. In other words, if the cash ticket is cheap, you can use Avios, but if it's expensive you won't find an award seat. For me, redeeming on Vueling is usually below my valuation of avios so I just pay cash, particularly when there are double avios bonuses...
I don't think Vueling are known for having wildly fluctuating fare prices, so you're unlikely to see the price come down too much...