You should not have to reset your Extreme at all. They normally run for months on end.
Several years ago there was a firmware update for the original, "round" AirPort Extreme that resulted in the need to periodically reset it as you describe, which was resolved by reverting to an older firmware version. Shortly thereafter Apple introduced the 802.11n Extremes, and subsequently the simultaneous dual band base stations. All Apple base stations are now simultaneous dual band models. If yours predates that model then an upgrade is justified.
40 Mbps download speed is nothing special. Even the earliest model AEBSs would not have presented a limitation.
A current production AirPort Express now has many of the advantages of the current production Extreme. The essential differences are: three LAN ports vs. only one on the Express, Gigabit Ethernet for the Extreme only, the ability to connect a USB hard disk drive (the Express's is for printers only), and the Express's AirPlay audio output. That's pretty much it.
My model is the dualband wireless N (not round) version. The mention of the download speed isn't meant to brag because no it isn't anything special...just didn't want any responses about people thinking I was misinterepreting bad download speeds for a bad router.
I might be misreading something here. The current Express has advantages over the Extreme? That doesn't seem to make much logical sense but I'm not too familiar with the differences, hence this post. I assume you mean that the current Prod Extreme has the 3 Gig ports, 1 x USB (2.0?), and the Express allows audio whereas the Extreme does not?
I guess what I'm asking is is there a hardware difference between let's say Wireless N model version 1 and Wireless N model current version?