The thing is, PS1 was pay to play. I was perfectly happy spending £7.50 a month to play the game normally. So with PS2, that's my upper limit on spending. I'm not going to buy stuff for the sake of it, but equally if there are going to be items and so on which alter the gameplay, then I will certainly consider it, because that's how much monthly I'm willing to spend on the game to enjoy myself.
Of course, it does depend on what they are offering. Exp boosts might be nice at the start to give myself a leg up, but later on I probably won't mind about it too much. And they would have to be careful to balance any 'stat' boosts, since if the boost isn't large enough then nobody would buy it, and make it too large and people will complain.
But looking at it realistically, its way too early to comment on it, without knowing what exactly the plans are. Of course they are going to sell stuff, they are a business, but it remains to see what.