Will increasing size of amp improve sound quality?

With your current speakers -- no.
As to upgrading speakers take a deep breath until you can go for Sonus Fiber Grand Piano.
With your current amp they will sound yummy.

Its true only if you have big woofers to get them moving or very insentive or low impedance speaker. I agree that the book shelves don't require any more power, get some bigger Klipsch. If you are a Klipsch fan you can pick up vintage Heresys with a 12 inch woofer (only the original heresy type 1 not the 2= pre 1982 for about $400 in medium condition) they like a little juice. Yes I know they are 94db per Watt at 4 feet (not meter) but its all midrange horn with juice, the woofers really give you their capability, great but somewhat rooled off and very tight bass its enough for me. Not good for for organ Music or classical if that's your preference. They will rock your heart out if you ask them to.

As a previous owner of several Rotel amps, the answer is NO. Move onto something else. I also agree with Drr, upgrade your speakers one day. Read the speaker topics for ideas.

Upgrade the speaker crossover networks will completely improve your speakers. It is easily the best thing I ever did for my audio systems.

I upgrade the Klipsch speaker crossover networks if you're interested.

Mike

Thanks to all of you who thus far responded to my question. I am so new at this that I am easily confused. I looked into the Sonus Fiber speakers. Which ones would you recommend? And, I wondered if they are priced by the pair or singly. Bartokfan mentioned moving on. Had you had a bad experience with the Rotel?