Talk:HYUNDAI I20 WRC/@comment-26363841-20160118031452/@comment-25956839-20160118100118

It depend on your goals, bonus series can be skipped and completed at a later date. See:
 * What are your goals in Real Racing 3? - Interesting forum post about goals.
 * User blog:RR3 Michael P/My car garage, upgrades and progress though RR3 - my progress and cars bought (May 2015)
 * Upgrades Strategy For 100% Completion - Upgrade requirements and rewards to get to 100% completion

Normally bonus series that require gold are left, personally I haven't completed this series after years of playing RR3.