Ari,
In essence, a Roth conversion represents the opportunity to choose to pay taxes now (when you convert), instead of in the future (when you would have withdrawn).
Which time is better? In the case of the traditional vs. Roth comparison, the most significant driver is pretty straightforward - pay your taxes whenever you think your tax rates will be lower.
So if you expect your tax bracket in the future to be higher than it is today, then converting is a good idea. If you think your tax bracket is higher today and may go down in the future, then hold onto your traditional IRA and wait to take withdrawals when those tax rates go down for you.
All that being said, there's a kicker that helps to encourage a Roth conversion in your situation - the fact that you apparently have some non-deductible contributions in your IRA. The Roth conversion rules only require you to report the value of the account IN EXCESS OF your non-deductible contributions as income, which means you might be able to convert the whole account while reporting only a fraction of it in your income for tax purposes (and only a percentage of that will actually be the taxes you must pay). So you're probably going to find that this is a good deal for you, as long as your tax bracket isn't unusually high this year.
The biggest caveat - be certain that you have the money available to pay whatever taxes ARE due as a part of your conversion. You won't want to take the funds out of your IRA (or new Roth IRA) - that can cause taxes and potential early withdrawal penalties itself, and to say the least will diminish the size of the Roth IRA you were just trying to create. So be certain you've got a taxable investment account or a bank account you can draw on to pay the tax liability!
I hope that helps a little!