one nr 1 is nothing at all for a real site a few dozen or more nr 1 pages then you may START think that you did SOMEthing right and how to get another few dozen nr 1 ... !!! then make sure they all are nr 1 in MSN, Y and G simultaenously to be sure you make all correct a few hundred top 10 is most likely normal among created content-oriented sites
So I am number one for 5 terms ... and one term brings in over 4 times as much traffic as the others combined. Not everyone will click the first results ... so I am thinking another top 10 placing (with probably a different summary) might raise the traffic for that term by another 10-20% ... which would be huge. From what I have seen top two results from the same domain will be "nested" .. yet if the second result is a sub-domain it would be listed as normal .. so my gut feel tells me a subdoamin is the way to go. If you domain already has your main keyword would an additional one from the subdomain be helpful also (example.example.com)
Please stay aware of the fact that you are getting close to spam there. I know domains like: http://example.example.com/example/example.php and those usually do not last long. Just try to get another SERP #1 just the way you did the first one. On similar topics or synonimes is more effective than to own the complete top10 of 1 keyword.
Depends what the #1 is earning you. If it's a nice earner, bring an internal page up as an indented result. If it's a brilliant earner and you have the resources to bring sub-domains or other sites in there too do so. Otherwise - just look at improving the conversions rate / earning from your #1 spot.
Yes ... Its such a fine line when it comes to spamming I would consider your example somewhat spammy .. but what about this .. phpexamples.example.com/php4examples/example1.php phpexamples.example.com/php4examples/example2.php phpexamples.example.com/php5examples/example1.php phpexamples.example.com/php5examples/example2.php ... etc
The whole key to all of this is what is your desired result? If you only have one product or service, then finding "other phrases" to come at it from a different angle may be the right choice. If you have other products or services on the same site, why not promote them to number 1 as well. Never forget the real reason why you have the site at all.
5 #1 is one thing but do they turn into sales? If so, another website might be a good option but if not, you might want to focus on turning this one into a profitable one before spending energies on something else.
I'd say it is easier to get a second #1 listing for the same site rather than for a new one. Of course, it depends on the keywords, but still ...