I've held an SEO theory for some time that is based around the fact that a search engine only has a finite level of resources (bandwidth, disk space etc.) with which to index the web. It follows, therefore, that rather than say "I will only index X number of pages of site Y", an intelligent search engine will say "I will allocate X amount of resource to indexing site Y". Therefore, if you can reduce the amount of effort required to index your site, you should (in theory) be able to increase the number of pages indexed.
One thing you can do, if you are running Price Tapestry on the PHP / Apache combination is to enable gzip compression of your pages. This means that the output from your web server is compressed on the fly, and then decompressed by the browser (or search engine crawler), thus saving on bandwidth - and because of this, Googlebot and other search engines might consider indexing more of your site as a result.
Using gzip compression requires the zlib library to compiled into your PHP installation (not enabled by default). To find out if you have zlib, create a script to view the output of phpinfo() and look for "--with-zlib" in the configure string. If zlib is compiled in to your installation of PHP, then in html/header.php, simply add the following line of code immediately after the opening PHP tag:
That should be all there is to it. To verify that the handler is having an effect, you can use the Web Developer plugin for Firefox. Browse to your homepage, and then use the Web Developer menu to select "Information > View Response Headers". In the headers, look for:
That will confirm that you have enabled compression, and could mean that with everything else being equal, search engines will index more of your site as a direct result!