It seems like infi2 havent receive any updates for half year already, if you havent give up on this game yet, read my suggestion catefully, it will boost your profit.

People dont like to spent money on numbers, instead we prefer getting something that make us feel exclusive!
Be smart, not to work hard!
This game has interesting concept, with sufficient content, yet it does not have good direction.
I can totally understand you want to make this game completely F2P, but you still need to eat!

So, heres my suggestion:

1. Should research changes tower stats, modifier stats, coins bonus, wave timer, mob stats, lives and bounty ?
   Hell No! This will give people an idea of P2W or grind hard game.
   So, what to do with research tree?
   Research should only changes the amount of tower/modifier/ability u can built, upgrades/level limit, craft queue, loot bonus, and mainly for unlock things!
   This will add progress while keep game balanced, a well balanced game can makes crazy profit too!
   Remove mystery dust, endlesss upgrade stats is just as meaningless as it sounds.
2. Custom map items need adjustment.
   Music Box: Stop dropping music box as loot. Unlock from research tree, thats it.
   Barrier: let ppl craft from material instead of randomly drop, else ppl not able to make their desire map unless hack your apk
   Base: Modify starting money, wave timer, lives only!
   Add configuration: Limit tower/modifier/ability amount by type
   Add share map function : registered user can share their map, one per user, purchase vip to increase slot(since it use ur server capacity), can be rated, if played by someone else, owner receive reward.
3. Ads, watch ads to revive(story only), refund 100% all coins but receive score penalty, help ppl go through story quicker,
   Watch ads to play a wheel for bonus resource after game, better look and feel increase amount of ads watched!
4. Finally, in game purchase, what will people buy?
   Exclusive items for custom maps, vip system/battle pass for more loot. Not simply numbers and expect people will buy it.
5. The rest can remain same as it is. Dont make developer console thing please, unless you dont need to eat!

So update it or make infi3 or whatever fast!
Let me warn you that you are not the only one who know how to make TD games from LibGDX in this earth.
Anyone including myself could just copy this game and my idea to rebrand as their own!