I'm very happy to see my favourite part of the game get some attention!
I would have a lot more to say if the Arena as a whole was getting a much-needed revamp but, I'll keep this brief since we're just looking at prize support in this topic.
So, let's start with gold.
There seems to be some misconception that gold arenas bring more gold into the game however, this is factually inaccurate.
Tournaments with gold prizes use the following formula 1500 entry fee for each 10000 gold
Each tournament starts with a minimum of 8 players
1500 x 8 = 12000
When you crunch the numbers, arenas for gold actually take gold out of the game.
Using this ratio, I think it's fine if we vary the gold amounts on show if the entry cost formula stays the same.
I personally believe that 2mill gold should be the new cap if the system can be tweaked.
Now regarding the option to convert arena tokens to gold, I'll be real and say until reading this thread I'd forgotten that was even an option because the ratio is so forgettable and bad that it's not even an option worth considering.
Unless it gets a significant increase, of course.
Potions
Now when putting in potions I will say that for me personally, occasionally having a convenience option for these comes up with the existing EW and FI 1k in the shop. So, for low-cost rewards I think the RF200 and Lesser Cloaks would be worthy additions.
To introduce anything truly new into the pool I think it needs to be 100 or 200 cost at a minimum, I think other users have put forward some suggestions that would be worthy additions of similar expected value.
Items
More gear is always more fun!
I'd like to see more crystal sets for purchase in the shop, regarding gear sets though usually 2 set combos give the best stats if you were to make a 3-piece set it would need to have significantly better stats in order to consider departing from 4 set + filler item model that optimised setups use in all aspects of the game.
The prospect of having some epics tied to the arena is exciting!
I particularly like the idea of them requiring multiple parts like the Ward/Steamwork/Hammer line although multiple tiers of them would be unnecessary if they launched with modern epic stat lines.
Another thing you could do is have alternate stat lines for epics as invent options.
... and that's about it! Thank you for consulting the community before making major changes, I hope that this dialogue can continue with future improvements!