Because the Civic is a great car for what you want, I'll suggest some options for that.
For road noise, look into different tires. Or else, refresh your suspension. The bushings probably need replacement. With aerodynamics out of the way, the main sources of noise are tires and exhaust. These are easily remedied.
If you MUST go 90mph, and doing so will lower your mpg drastically, concentrate most of your energy on aerodynamic mods. Browse some Civic builds here, especially basjoos's
Aerocivic - Honda Civic modifications for maximum gas mileage - aerocivic.com and begin improving. A boat tail will get you great fuel economy, but it's a lot of work (3 weeks and about $500 for mine- 46% better MPG @ 60mph). Start with wheel covers, rear skirts and air dam... then think about a boat tail.
TDI's are great for economy but they are quite expensive used.