There's no real drawback to using up your bouquets, actually. When it comes to spirits and affection the best advice would probably be to check out this link as well as the Daily Missions other posters have already mentioned. As you can tell from the chart there's a lot of maps where any benefit you're gaining from using higher value gifts is undermined by having to pay more Stamina to farm them to begin with. Ultimately your big decision will likely be based on the spirits you need more than anything else. Farming Low Cost Battle & A Gigantic Enemy is tedious compared to Phalanx 2 but it's often a strong option for newer accounts that still rely heavily on Silver & Gold units.