How do the Elac Uni-Fi UB5s compare to more expensive bookshelf speakers?

I understand your desire to change the sonic character of your system via speaker change. Serves as one of best ways to explore and discover which sonic characteristics are most important to oneself. After that one can then improve on the quality of the desired presentation with the purchase of a more refined speaker having the desired characters. From reviews do you get the impression that the Elacs are brighter than the Wharfes? If so maybe you should give them a shot.  

With your amplifier you are positioned for speakers that are more refined than the Wharfdales or Elacs. Of the speakers you mentioned, I have heard and really like the Dynaudio X14s. They sometimes come up used here on AG. I intend to purchase a pair myself when a pair comes up at my price. 

Even tougher. Just found a used pair of the finished slim cabinet Elacs for $600 on Amazon. I could get those tomorrow.

At or around your price you can get a previously owned pair of Revel M22's . Reference quality sound for a very affordable price.

If you have the funds to get the ELACs from Amazon now, then I'd do that and take a good listen for yourself. Amazon has an excellent return policy so you've got 30 days to get a feel for whether they are for you (in your space, room matching should not be overlooked!). If not, return them for a refund and save up for some KEFs. 

I own the Wharfedale 10.1 and 10.2.i heard the Ls50 with ML 100 w, accompanied by audio research preamp and theta transport n dac with aq diamond ic n dragon sp cables, they blew me away, this speakers are capable of giving you anything you connect to them, there's limit of course...
The Elac UniB5 I heard at Axpona last year, connected with Audioalchemy gears n Audioquest cables, they also sound very very good.
So which one to choose? If you have budget and good gear Ls50 is the way to go.this is a quality speaker...well made, well built...The B5 you can't go wrong as well...no matter what they are musical...