Hey super fun. the exp slows down a LOT when you get to lvls like, 60 onwards, which may be intended. Also, because they give diminishing returns, i think itd make more sense to just cap all the skills at a certain level. Maybe not greed or glitter, but the heat and breath control ones should just have a flat cap if the intention is to prevent the player from having a non stop breath attack. Also an upgrade to increase the rate at which the enemies spawn would be nice. near the end, id just be waiting to get enough kills to fight the boss, without being able to afford treasure and not enough xp for it to really help in terms of damage.
I actually got really far and completed the bloodline upgrades, but mostly because i would get to around the dragonslayer and then the game would prompt me to lay another egg to upgrade and get farther faster. but then once i had fully upgraded, there wasnt much point in starting again, and the exp still slowed way down. I was only getting to level like, 50 in the early stages. I think i got to 80 on my most recent one with the bloodline maxed out but it still slows way down.