Ah.. as much as I really love the idea of this, I did some fun math and have my own little suggestion..
Sorry about the length of the post, but it contains some background, math and a suggestion to solve this "real money vs. chits" problem.
If you really want to use these coins for the purpose of replacing all the money in the game with these, for a party of 4 people, you would have to fork out a lot of dough (Using King of the Castle chits):
Level 7 - 130 USD
Level 8 - 185 USD
Level 9 - 257 USD
Level 10 - 348 USD
Level 15 - 1344 USD
Level 20 - 4928 USD
So - in conclusion, I dont think one should use them for that purpose with the current pricing of items in the game. With that in mind, I tried figuring out how I would actually use them and I ended up with this potential solution:
Use a higher conversion rate than 10gp=1pp such as 100gp=1pp or even 1000gp=1pp. Since all prices in the game are in GP, this could work out very well.
Of course, the trouble with 1000gp=1pp would be that if you give out an average encounter reward at, say, level 7 - it would be 3 platinum pieces. Not exactly an epic feeling to get three coins, regardless of the denomination. One could of course mix in gp-chits into it, but that would still mean the need to buy them (a lot of them...)
100gp=1pp is better here - a healthy balance between the two. A reward for a level 7 encounter would be roughly 30 platinum pieces. Buying 2-3 packs of various GP-chits would solve that issue.
The trouble is that King of the Castle chits don't have 1PP chits. Paizo does - but those packs come with 4 chits of 1,2,5 or 10,50,100 PP and costs around twice as much.
So I figured I would think about how much money - realistically - my players would end up having stashed in total as a maximum. I came up with a couple of figures. In any given campaign, I expect my players to never have more 150 000 gold but of course that varies from DM to DM.
Here are some recommendations if you want to use this idea and what to buy for "the bank" for a party of 4 players:
200 000 gold per person: (~276 USD)
3 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8aro
3 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arp
5 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arq
12 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arr
150 000 gold per person: (~228 USD)
3 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8aro
3 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arp
4 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arq
9 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arr
100 000 gold per person: (~192 USD)
2 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8aro
2 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arp
4 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arq
6 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arr
75 000 gold per person: (~144 USD)
2 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8aro
2 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arp
3 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arq
5 packs of http://paizo.com/store/gameAids/other/campaignCoins/v5748btpy8arr
Since I run a game with 6 players that are currently around level 7 I don't think I will end up buying these, I rather spend money on maps =)