People vote for Farage because the only difference between MEPs is how much of a symbolic protest against the Commission they will make. There's no other difference: it's not like an MEP can introduce a bill to change freedom of movement or reduce the EU's budget.
So the UK sends Farage. He achieves nothing. Nobody cares, because nobody expected him to achieve anything anyway. No MEP could.
Yes you are right. Political parties need to present a Euro agenda that their representatives will commit to advancing. Currently we only have the false dichotomy of (a) do what Brussels tells us or (b) tell Brussels to GFT which really isn't good enough. Sending the prime minister over there every 6 months or so to "get concessions" that the representatives should have been coherently campaigning for in the first place doesn't count.
So the UK sends Farage. He achieves nothing. Nobody cares, because nobody expected him to achieve anything anyway. No MEP could.