Every few minutes would eat your bandwidth very fast The more backlinks you have the more often your site will be crawled. You can also set your crawl rate in your Google Webmasters Central account. Also, keep an updated form of your XML sitemap always, I believe in my opinion this helps Google crawl your site faster when it bounces to it.
If you change your content quite often then google will spider your site often. This can take a few months to kick in but it will recognise the fact that your site is constantly updating and will spider you more regularly. More incoming links will also help...Again you need to continually add links. Use directory links but add them slowly so google finds what it sees as more links every time it spiders the net, it makes it look like you are gaining links and the spider will visit again.
Ping your updated article. If I was not mistaken, it will take 10 to 30mins after ping. search on the web for ping sites.
Links in forums sig will make your site crawled frequently and building more links. Account in google webmaster tool can also help.
The spiders follow links, the more often they find a link to your site, the more often they head back to your site However, I think the spiders may find it easier to re spider smaller sites, than bigger sites unless you use a very accurate sitemap.