I really like this suggestion. Could use tweaks and balancing here and there but the core idea is well presented. The problem is obvious and everyone is aware of it. Arena is just not worth doing at it's current state, not even for beginners. Sure they can get upwards of 60k tokens but that is extremely rare. Most of my runs I get around 20k as you stated. It definitely does not feel rewarding running around for over 20 minutes shooting mobs just to get that little in return, not to mention it gets extremely tedious and boring. I especially liked the part about random events during the arena brought out here:
My main issue with arena is that it does not provide enough tokens. I usually get more on wave 5 than wave 8 or 9, even 10. With your change I am sure arena would be worthwile in the form of increased token rewards. If, however, none of your suggested changes are to be added into the game. I would like to suggest to at least add some sort of kit boosters since it is virtually impossible to play arena solo past wave 7 without running around endlessly and abusing mob AI. The kits deal too little damage, it takes over 5 archer shots to kill a mob and there is 40+ of them. Now, some could argue that arena also grants money but the amount of money is extremely low. Next, there are books of which 99% are Eff For or Unb so that aspect falls short as well. An additional idea could be to buff the chances of LuckyMining and other rare books after every boss wave. This. of course, is in addition to buffing kits since nobody is getting to wave 10 alone with current ones.
To sum it up, overall an incredible suggestion that I would personally, as well as many players I reckon, like to see realized and implemented. Arena is an amazing feature on the server and I would like to see some more light shed on it and more work put towards improving the arena experience.
Kind Regards, Pickle