Hi Mike, nice change. I've actually implemented query result caching in XCSEO Pro to avoid situations with the same data being fetched repeatedly. I'm also investigating other improvements, such as building an array of all urls that need replacing, and build one-time queries that would fetch data for everything that needs to be replaced.
Any improvements that I come up with in Pro, that can be backported to basic, I'll backport.
BTW, while your method definitely improves performance, I do prefer to avoid having to edit template files. I've found users often have their skins replaced, or add mods that replace changes that have already been implemented, etc, more so with tpl files than php files. While you're a savvy user, and obviously know your way around code, most users aren't, so XC SEO basic is aimed at the "lowest common denominator", in this case.
But I appreciate your feedback, and I'll keep it in mind when making other changes to improve performance
Ideally, I'd rather modify the function in X-Cart that pulls back product data, to cache that data to be globally accessible, same for categories, etc. There are multiple occasions when X-Cart itself queries more than once for the same dataset, and having that info cached already would be nice. Maybe I could develop that as a separate performance patch (would have to weigh the memory use against the benefit of less queries), and have XC SEO check for the existence of that performance patch, as an added optional speed boost.
EDIT: just as a note, I've worked on proprietary code before, that functions as a cache class. You could flag cache data as session based or persistent, and if persistent & memcache is available, the persistent data would be stored in memcache. That would be nice to have developed for X-Cart