One particular year, I was trying to make a catchphrase out of "Read the manifesto!", which was short and snappy but edited to the point of losing the nub of the message which was "Read the manifesto... this time."
Also that left it unclear that I meant people should read the manifesto of the party they intended to vote for, not something I'd written myself.
Along the lines of what you're suggesting, I'd want to repeat this message but with one key alteration: Read the manifesto from the last election. Ask yourself "Have they delivered" before wasting your time on their 2015 promises.
Gromit's recent thread (featuring extract of Osbourne speech) got there first, though.
Aside from that, we have news media reporting on Party performance, we have Political Party websites for manifesto documentation, we have Wikipedia for longer histories, we have Bloggers for comment and opinion and this is AB, for those who are at a loss to form their own opinions, based on that lot.
:O)
Ultimately, though, when I took my own advice and saw just how many pages there are in a typical manifesto, I decided that I didn't have two or three hours to throw away on something that dull and didn't bother. I can't even practise what I preach, on this issue. :-/
Hence, we're reliant on the newshounds to *actually* read this material and pass it on to us, in digestable form.
A simple choice, then, between being at the mercy of Murdoch's minions as to how our opinions of political parties are shaped or spending actual hours of our free time, reading them for ourselves (strictly for masochists, I suspect).