If you are already listed in the search engines, can you resubmit it yourself once you have made changes to optimize it better, or is it best to wait for the spider to visit you again? Sorry if this is a stupid question!
No need to submit again, get some links to your website then the Spiders (bots) will find your new Content and index it automatically.
just wait, no need to submit your site to search engines at all. also it's not recommended to submit your site to google, google will find you if you have back links that point to your site
Yes, it is good to add fresh & useful content and let the search engine find you rather than submitting it again.
if you submit your site again and again, search engines will consider you as a spammer and they may delete your site
Actually, they'll just ignore you. You only need to submit your site to the search engines once. I strongly suggest doing it when your site has been finished. Submitting a submission request simply says "Hey, I'm here!" to the search engines. Their spiders will get to your site when they feel like it (the proper answer being once they get to you on the list of sites they need to spider - at least that's how my search engine works anyway).
That's a way you can get banned/deleted. Build quality, strong backlinks and add some fresh content to your website, and keep it updated and the spiders will crawl your website w/o resubmitting your site. Meti