Cisco ASA 5505 or 5510

What are the main advantages of the 5510 over the 5505? Does it justify the extra $1000+?

We are about to host our own site, and currently, the plan is to just have the web server on our internal network behind a ASA 5510. However, for the same price, we could set up a 5505 and a 2811 or something, and then have the web server on a DMZ between the two devices. Is this a better idea or should we stick with the 5510 plan?