Being that you are in Michigan, you will probably require an air pad with a higher R-Value, unlike me here in the Southeast that can get away with using an original NeoAir (R-Value 2.5) just fine down into the mid to low 20's (F). If it gets any colder I can simply layer a Gossamer Gear 1/8" ThinLight pad on TOP of the NeoAir and survive anything around here.
I would suggest for you, going with something with an R-Value of around 4 - 5 if you plan to use this one pad year round. This should be fine for your warmer months on it's own, and then as I mentioned, you can layer a ccf pad on top to boost the warmth (and even the comfort IMO).
It is important, especially so in the cold, to have adequate insulation, both on top of you as well as below you. So, if your top bag does fine for now, but your bottom is a little lacking, you should replace the bottom first. But, if the bottom is just slightly cold, by getting a ccf pad to add to it can be a cheaper alternative to replacing the whole pad. Something to think about...
As far as your statement about someone getting cool with a NeoAir and a quilt, well that is a vague statement and not one that can necessarily be relied on out of context. Given the appropriately insulated top quilt with an appropriately insulated bottom pad, one can stay snug as a bug.
However, a few other things to think about that affect staying warm on a cold night... make sure that you have eaten appropriately so that your body doesn't run out of fuel during the night. Your body is a furnace and requires a fuel source to continue to produce adequate heat, which is food and water.
Also, make sure that you void before laying down, and if you have to go in the middle of the night, get up and go. Don't hold it. Your body will be using up that fuel source to help keep the urine warm. So, jump up and go pee, and then do a few jumping jacks before crawling back in to get your blood pumping!
Make sure that your sleeping bag/top quilt fits you appropriately. If it is too big, your body is trying to heat all that extra room, if it is too small, your body is pressing against the sides and compressing the loft, which is what holds all that heat that your body produces close to your body. Less loft is less storage space.
Make sure that your pad is inflated. From what I understand, the R-Values that are listed for sleeping pads are based on the pads being fully inflated. If this is true, if the pad is barely inflated, then you are only taking advantage of a portion of what the pad offers. (Although if I am wrong here I am sure that others will chime in. Like I said, I have read this before, but cannot confirm it.)
The amount of clothing that is worn inside a bag seems to be a bit controversial by some. Some will sleep in layer upon layer of clothing (everything that they have) inside a sleeping bag, while others wear a thin baselayer only, and then there are a few that sleep in the nude. Of course the argument for wearing everything is that you are distancing yourself from the outside air and providing more air pockets to trap the warm air that your body is producing. On the other hand, if you are layered up, then none of the heat (or at least most of the heat) that your body produces does not make it into the insulation of the sleeping bag/top quilt because it is getting trapped in the clothing layers. If this is the case, then there is more cold air trapped inside the sleeping bag... So, my suggestion here is that you try it out (even in your back yard) and find the combination that works best for you.
As far as a quilt, if you are using the quilt on the ground, width is an important factor. When looking at these make sure that the width at the shoulders are adequate to wrap around you without compressing the loft. As a reference, I am 5'10" and 195 lbs. I have a top quilt I got from Hammock Gear. It is 49" wide at the head end and has a straight taper down towards the feet. As a side sleeper, this is really too narrow for me, but it works ok because this is a summer quilt. if I were looking for a quilt to use in temps below 40 F I would want something with at least 52" width at my shoulders, and would be happier with about a 56" width (however, this is my preference, you or the next person may have a different preference). Quilts are a great piece, but they are not as simple as a sleeping bag, at least not until you use one a time or two and get an understanding of them. However, quilts are typically lighter and pack up smaller than bags, so they definitely have their advantages.
Also, if you decide to layer a ccf pad with your air pad, I suggest putting the ccf pad on top of the air pad rather than under it. Reason being, when you lay against a ccf pad, the warm air does not move away as easily when you roll over as it does in an air pad. In an air pad, movement will stir that warm air around inside the pad with cold air. So, keep the ccf pad on top of the air pad to gain the most additional thermal efficiency of the combo.
Anyway, I hope that this helps. And of course feel free to ask away on here...these forums have all the info you need and can be a lot of help if you ask around.