You're going from the ultra-low end from 2001 to ultra low end in 2002 (technically, the 5500 wasn't out in 2002, but this is a card very comprable to the much maligned 5200). This is not going to give you a huge performance boost.
You're going to double your shader power and pixel fill rate. Source:
http://www.gpureview.com/show_cards.php?card1=158&card2=127
Everything else will remain the same. It's almost impossible for directx7 codepath games you're playing now to be limited by pixel shading. So you *may* get slightly higher frame rates. But, it's more likely the performance will remain identical if you're limited by memory bandwidth (possible) or texture fill rate (highly likely).
Save the cash. You can find a 6200 in AGP, and with some luck that'll unlock to a 6600. Or you could save up another $20 or so and get a non-GT 6600 for around $60.
Another possibility is various Radeon 9600 cards, which hover around $45 every so often. It won't be much of an upgrade, but you will be playing circa 2002 games in style.
edit: It's not a 'new' graphics card. It's an old graphics card, from the extreme 'value' segment. A lot of cards in this category are not that much better than integrated graphics.