Most of the items in there are for convinience I guess when there was less of them in the ECO... its easier now for people to just buy boosters, quick sell for gp then buy all the other items in the ::store now and have change left over, which is actually lowering the price of boosters too!
IMO this would help so much, being able to advertise a "BUY" offer on there is a significant improvement.
Playing devils advocate though...
It could see more of the 'wealthier' players being able to buy everything for example:
Less wealthy players wanting to do some small level merching, like buying an item for 4m off someone who needs quick cash, then selling it at a more prime time for 5 or 6m would totally go away given there would more likely than not be a buy offer in the TP for it.
I think it would definitely minimise trading / merching / deals / bundle sales and interaction between players in the eco side of things.
There is absolutely nothing I can suggest being a downside of being able to buy with platinum tokens, this should be in-game without a doubt !