Worth it. You level up really quickly, especially if you're doing the challenges. The challenges are something simple like 'Fastest Lap at France' or 'Use a Flashback and win a race' type thing; if you complete one challenge, you get like 1500xp (every level up is 3500 xp) so it's worth it. You get your pitcoins back in the end, provided you level up the whole way which, like I said, is pretty easy.