One merit might take a while to gather, but it's not unreasonable to ask before being promoted.
For the new merit sources, perhaps they could be given the guidance to focus specifically on accounts with 0 merits (and a quick review of their post history). That way new members won't get frustrated, since they should receive a merit relatively soon if their post history is "normal".
I don't think that "buying" older accounts is a problem necessarily. If moderators ban spammers, it's a lot of money to keep buying new accounts just to spam.
1 merit is simple to get. It's hardly a restrictions for half decent members, and with the newly added merit sources there should be a lot more merit being distributed. Spammers don't change just because they have bought an account, and are usually banned or found out by the scam busters of the community.