They're designed specifically for late-game players and not intended to be farmed quickly at low / mid-game levels. Once you build up to a guild that regularly does 40+ stars on LS and DSTB the farm is fairly quick (if you completely ignore gear and other character shards in there).
Like everything in this game you're presented a choice on how you want to progress through the game. I see those options as follows:
1) ignore everything in that store and farm Hoda and Wampa - this gives you an advantage over other players that started the same time as you for arena / HAAT & Pit, but provides a disadvantage in that you have less depth in your roster because you spent currency that could be used to gear your toons on character shards
2) you ignore those two toons and farm gear. this provides you a well rounded roster that provides an advantage in TB, TW, and HSTR. Really, any game mechanic that requires a large, well geared roster of toons.
My advice, ignore them until you are around 2 million total GP. Farm as many MKV Stun Guns as you can from guild event store. Gear your ideal arena team and legendary / hero toons to G12 (dont worry about the G12 gear unless you must). Start farming Hoda or Wampa and focus 100% of Guild Event Tokens on that character until they're 7*.
For reference, I'm 3.3 million GP and have Hoda at 7* and Wampa at 6*. I focused on gear for a long time and now I'm exclusively farming Wampa until 7*. It's frustrating because there's obviously a gear crunch, but i stay focused on my goal because trying to do both would just make both farms longer.