NEW YORK ( TheStreet) -- What do suddenly cash-flush U.S. investors do with the extra dollars they're earning these days in their investment portfolios? They're spending it, not saving it, and putting the purchases on their credit cards. SaveUp, a San Francisco financial rewards-based services provider, tracks what Americans do with their portfolio proceeds. And in July, SaveUp says, the average investor saw asset balances rise by $369.64, mostly because of a "strong stock market," while 401(k) accounts saw assets rise by $1,848 for the month and taxable investments jump $1,926. Finally, money market accounts rose by $207. gained 5% for the month? Maybe because the prevailing sentiment is that there is more where that came from in the financial markets, as Americans see continued gains for their stocks and bond investments.