I think the law of diminishing returns is appropriate here.
Car with 100hp is not half as fast as one with 200hp.
And going back to the original question, does a more powerful engine require a stronger, thicker chassis? Well it depends, if the engine is going to try and twist the chassis then yes. But the fact that the chassis just holds the bits together, then it doesn't matter how powerful the engine is. Using a 45hp engine doesn't mean you can get away with a chassis made of balsa wood.
And some of this boils down to Pub Talk.
My good friend wanted a kit car and at the time he didn't know what he wanted, so we talked about engines and chassis types. In the end he went for a Viento (the biggest) he went for a Rover V8 (massive engine) but then went to a 4.2 semi race tuned engine with huge carbs. Massive 17" alloys with low pro tyres. All parts of the car were 'bigger and better' and to me it lost its appeal. I want a small, light 7. Not a huge bling car. (Mark, if you read this, I'm sorry, I don't mean it
).
And I think this mentality is still here, if someone thinks 150hp is enough for a 7 then the next person says 'well I'm having 200hp' and then the next say 'well I'm going for 250hp' then the next says.... well I think you get my drift.