[Travis]

A hybridized approach may work for you in those higher periods. Depending on your bottlenecks, it may be possible to spin up ec2 instances during your high load periods that will cover your necessary additional capacity. (Esp if you are bw or RAM limited, you can setup asset servers on ec2 and just change DNS pointers to enable them.)

One other advantage is your future scalability, as well: as your site grows, you'll need to "resize" your dedicated instances. If that is something you need, then that's another advantage (really, it's continuous ability to scale versus discrete scaling events, e.g. upgrading a dedi server).

That said, if you have a good dedi provider, upgrading those shouldn't be too tough.