Well, there are many ways to get 1 or 3 day XP boosts.. and everyone certainly misses the almost consistent XP boosts our first few months.
Daily quests - every 5 days you complete, you get a 1 day XP boost, and after completing 55 advanced quests, you receive a 3 day XP boost.
CvC - there are a lot of XP boosts alloted for Clan milestones completion, and personal rewards (when we have them. )
Faction wars - These XP boosts are rewards for accumulating stars in every crypt altogether... but they are spread so far apart, its hard to tell when you might come up for a 1 or 3 day XP boost.
There are other ways in which you can receive XP boosts in different content, but if you want to remain boosted 24/7, then you might have to spend a cpl gems more than often. I recommend getting the daily gem pack, I keep one active on my account and usually never run out of gems unless I buy masteries, which I don't recommend doing but thats just me. Lol.