Sorry guys, !!DO NOT USE OLD CONFIG FILES WITH NEW VERSIONS!! whilst they may appear to work there can be hidden problems that wont manifest until after some use, also, old configs can brick the router.
For example, DD-WRT services change occasionally, if you have set a configuration for something that is later removed, or has its behaviour changed, then it can confuse things... A LOT of changes have been modified since r20025... It's nearly 4,000 revisions out of date!
If you want to risk it, you're welcome to try, but i personally would resort to pen and paper for remembering config version to version and updating ONLY when you need to fix a problem.
The post r20025 firmwares fix a lot of issues with the Buffalo version and i have improved performance drastically simply by updating, but if everything works for you, please do not update... Sometimes reliability is better than burst or maximum throughput...
As to features, there are several service improvements and config additions to the standard Buffalo firmware, some may be useful to you, others may not... Biggest fixes for me were for SAMBA and the NAS features... I also have more options under Wireless Advanced settings and some nice ad-blocking and filtering functions under services too...