Difference depends on some factors:
1) Protocol used. If your using a 1 1/2 old laptop, probably its a Wireless b or g used. So, check your specs of both your laptop and the adapter. It improves if your usb wireless adapter is much higher compared to your built-in wireless antenna. order by speed and range : B – G – N

2) Range. Two same wireless adapter doesn’t actually improves your range. unless one is higher compared to the other as described by #1. So as to your problem of getting 1-2 bars of signal, your obviously far from the access point. strength of signals you receive doesn’t actually depend on your adapter, it depends on your proximity and line of connection (if there are walls or something) to the access point and the range capability of the router/access point.

3) Share of bandwidth. Having two same adapters, i think, may have an advantage against computers having a single adapter. For the reason that you may have increased your chance of getting data signals emitted by a wireless router. But, for speed of downloading/uploading, i think, the difference is not noticeable.

4) handling of OS. It still depends on how your OS or a software/drivers handles two network adapters attached. Server OS’s optimizes the use of two network adapters compared to non-server OS.