You ask a very complicated question.

What does your wall assembly look like -- ask the builder if you don't know. You should have insulation within the wall cavity, and insulation between the wall and the siding.

Air sealing is just as important as insulation so I would ask about it too.

Is a blower door test required where you are?

The image below is from buildingscience.com. Lots of good info there if you want to read up on insulating and air sealing.

In a cold climate, insulation overhead is very important, and I'd upgrade there before upgrading wall insulation.

As Mark Bischak said, you have asked a very complicated question. It depends a lot on the design of your house and specific climate, and your architect and builder should be providing input.

In our recent addition we used open cell Icynene spray foam because it got the R value we needed in the 2x4 walls (no space for 2x6's) , but was less expensive than closed cell foam. We also used new foam insulation to convert the entire attic to conditioned space. This made sense because its an old house with substandard attic insulation, and when they added A/C they put the plenum in the attic. Your new construction house, in a different climate, would have different requirements.

Bruce

In Utah, elevation would probably dictate the best answer. Insulating any space from the garage is code so you don't really need to worry about that. Interior wall insulation is minimally helpful for sound and nothing else.

In "semi-custom", the correct financial answer is probably not to upgrade because your upgrade charge is too high. The correct environmental answer is almost always to upgrade. Which answer do you want?

If you have external insulation, it would definitely tilt towards not upgrading. I am guessing it is unlikely that you have external insulation - ie foam on the outside of studs - but it is worth asking.

What are the costs of the upgrades? As you increase r value, the rule of diminishing returns comes into play.

The minimum attic insulation should be R-30, and preferably R-38. Exterior wall insulation of R-19 is fine for your climate. I don't see the need to spend money on an upgrade.

Is the garage unheated? If it is then the floor insulation would be a requirement and not an upgrade. Does this builder have a long list of expensive upgrades?

I agree with other posters that the design of the wall assembly needs to be considered before making a recommendation. You would also need to define what "worth it" means to you (e.g., enhancing comfort, doing my part to save the planet, minimizing heating/cooling costs, etc.)

Insulation R-values are measured in laboratories where test assemblies have been built according to the manufacturer's instructions. You can directly compare the R-values of different batt insulation because they've been evaluated under controlled conditions.

Now let's shift to the real world: batt-type insulation is not likely to be installed according to the manufacturer's instructions. If it were, your insulator would need to charge a lot more to split batts around wiring and carefully fit them around receptacles and switches. And he'd need to staple the tabs to the face of the studs after which he'd get hate mail from the drywallers who would copy the builder on the hate mail and, well, you get the point.

Blown-in insulation is much more forgiving in the installation and will give better performance than a batt with an equivalent R-value because of it. You can always add insulation in your attic, but you only get one opportunity to insulate the walls.

New construction?

I would include a plan for Radon Gas testing & mitigation as well.

IMPO

SR