At times in the past, I've done something similar: rated various ideas 1-10 on things like:

  - ease of build
  - viral potential
  - level of maintenance required after launch
  - revenue options
  - etc

Then weighted each if necessary (e.g., maintenance might not be a huge factor if you have someone willing to help with that) and ranked ideas on their overall merits.

Of course, I could've probably got part-way through building one of the simpler ideas in the time it took me to rank the rest...