We could debate the nuances all day and it would only be speculation and opinion after all.
The LibDems are notoriously good campaigners and there is some evidence that many of their supporters have returned to them after turning their backs on the party immediately post 2010, after the shock of them entering the coalition.
Many now think that its the LD's who have been the success of the coalition, having acted in a grown up, restraining way often against the ideological hysterics of their coalition partners. It has to be accepted that despite the rantings of the political press (which has actually imploded on the left and right and helped the LibDems no end) the idea of a coalition has become more acceptable to the voting public.
Wheels is correct there are at least ten seats that the Libdems trail second, but only in single figures percentages. Wheels mentions Watford, but there is Oxford, Redruth, Hampstead, Harrogate,Truro, Newton Abbot and 4/5 others that I can't recall. The LibDems could take some of these seats.
This is why despite the polls I say a target of 40 seats is not unrealistic.