It sounds like your question should be... "Are Google App Engine's FREE Quotas 'enough.' The limits you are describing only apply to App Engine's Free Default limit.

For example... for requests, the billable limit is 14,400 GB per day maximum, with a maximum request rate of 10 GB/minute. There is no Incoming Bandwidth limit when billing is enabled.

I think the question you should ask yourself is "what type of application do I want to build." If you have application requirements that you think will exceed the default free tier, then you should plan your budget accordingly.