Speaking for myself, I would happily drop £100-200 a year on Neo if I thought it would bring me more fun. I spend about £200 a year on games already as I play PS5 games (AAA, not bothered by indie titles) and KingsRoad (a browser/mobile) game. I used to treat myself each Birthday and Christmas to £50 on a free-to-play game but I haven’t done that for ~3 years since KingsRoad hasn’t been worth spending on and Neo has never been.
What I’d look for is spending ~£20 for a fun monster that is otherwise not available. I’d also consider spending for a bundle of legendary potions, e.g. £5 for 10. I’ve had a few other ideas but can’t remember them now.
In KingsRoad I didn’t spend for the first 1.5 years of playing. In that game you build some things slowly over time and spending can help speed it up. With that setup I choose to play for free. What got me spending was they brought out cash deals for some unique and powerful items plus occasionally I’d spend on some “stretch goal” where you can get most of the way for free / with gems and I didn’t have enough gems at the time so I bought some. I think there’s a lot of opportunity for Neo to do similar things where they occasionally give bonuses in eggs for buying X packs so it encourages people to open that many.
KingsRoad did a good job of targeting things at different parts of the playerbase. Some huge bonuses for spending big, powerful and unique things for spending small (e.g. £20-30) and a few cheap grabs that a lot of people will get (e.g. £5 for 10 6* pots). Right now all Neo does is give benefit to people who pour loads of money into the game, from what I can tell.