Can I fertilize w/SBM and Alfalfa and hope that the lawn will thicken and spread?

You could, But I think it would take to long.

Why dont you want to put seed in the bare spots?

This is right in the middle of my front yard. I was just worried that the new grass that would come with reseeding will stick out in contrast.Also, since I would hvae to aerate bnefore reseeding, I was a little concerned that may little ugly right in front of the house...

I was just worried that the new grass that would come with reseeding will stick out in contrast.

If you get the same type/blend of seed as you currently have, you will be fine.

Why not overseed the whole lawn? Now is the time!

The temperatures are in the high 80s for the next 5 days.I guess,thats ok for overseeding?
Also, should I ferilize before/after overseeding?

Whether your grass will refill depends on the grass. Some grasses will not refill without seed. Fescue is the most popular turfgrass that does not spread. Actually at this time of year, spreading isn't going to happen anyway.

Assuming you are on an organic plan, you should use alfalfa or some non-corn product about 2-3 weeks prior to seeding. Water the bare soil as if it was living because it is.

Seed heavily over the entire lawn to have a dense turf by spring. Then avoid watering frequently as much as you can in the spring to keep from sprouting the crabgrass seed. Keep your grass tall and you should not have any problems.