I actually enjoy having solely the random factor, especially for collection kitties - to me, it's like a giant gacha and the toys/teacups are the "super rare" marked items beyond the "rare" versions of the collection kitties such as the Painted Possession, etc. It's exciting to test my luck and hope for the best, there's also a handful of people who loyally collect sizes and it's fun to have that group to exchange stories of our quests for grail toys and teacups.
I'll be honest, I rarely bought any starters this time around because there was no size gacha factor in Vday 2013 and I think I'd be less prone to buy if vitamins simply removed the quest factor involved with every release. It does get frustrating to not get a toy/teacup when you want to, but it's so much more rewarding (and fun!) when you quest and hunt down that extremely rare dream kitty or are lucky enough to get it from the gacha, whether from your own breeding or the main store. The quest for that grail kitty also gives you a chance to meet and interact with others, which is what this community is all about as we share our kitty experiences and help one another out.