Yes you can spam with urls. Keep repetition under 3 occurrences in paths.
Length is still important. It depends on how you think people are going to find the site:
a) is this a site with heavy updated frequently content? eg: is there going to be a high repeat rate? Then length of domain name is most important and people will type in the url and remember it.
b) site designed solely for products? Length of name is less important than the "catchyness" of it itself.
c) mix of a and b? make sure the primary keyword is in the url, but make it catchy. aka: webmasterworld.com
d) is the site going to have children in the future? look for a common kw that can work on the children as well. aka:searchengineworld had a kid webmasterworld, and the name of the next one is seoworld but still just a gleam in my eye ;)
I think it is important to shoot for something somewhere in the middle. If the domain is a customers of high value, I go through a pretty elaborate process.
The start by brain storming to death on potential domain names. Sometimes I come up with mega lists of 4-5hundred potentials (think Oingo whois).
Then go through and rank them by length, kw value, and the rejects. After "whoising" them to see that they are available, I make lists:
1) length of name.
2) kw value of the name.
3) rejects because of potential spelling errors.
4 "quality" of the name.
The 4th one is tricky because it is just a visceral gut reaction to the domain name rolling off the tongue and fingers. "Does it look, type, and feel ok? Am I going to feel good about having that on a page?"
From that, I take the top 10 domains from the top 3 lists and make the final thirty. From there I start to investigate each name for potential conflicts. I do se searches on the domain name to see if someone has anything similar or if it is perchance a brand or product name.
After weeding, the final cut is always a gut guess on how the domain looks and sounds. Sometimes the keyword combo wins, sometimes the better "looking" wins.