Against my better judgment, I'll dive in here. The OP would be very comfortable with A. T. Mahan's The Influence of Sea Power Upon History (The case for why the US needs a strong Navy and not much of an Army).
Opinion is yes there needs to be a regular Army (with a different focus), an Army Reserve, and disbanding the National Guard in favor of the Militia.
Reason behind my opinion is the following:
Regular Army should be a General Staff, Training, and maintaining full strength Brigade, Division, Corps, and Army headquarters (these also serve as the training cadre for the Militia), and a few full strength units based on threat analysis, and the need to give NCOs and officers actual experience in operating units - this experience is needed to maintain a good training program.
The Militia is intended to be the primary building blocks for the National Army, should one be needed. One of the big problems in a militia structure is the quality of the unit, which determines the training time required to make the unit combat effective. You can draw experienced officers and NCOs into the militia units from former active duty people, you increase the ability of the militia unit, and shorten the training time required on call up. You can relatively quickly build support units if the equipment is on hand. Driving a military truck is not much different than any other truck, medical skills readily transfer to a military application, and the same for engineering and other support tasks. The combat arms skills are critical to military success, and this requires study and training is those operations, and some experience in order for leaders to make sound decisions. Computer simulations are not the same as actually doing it with a unit. Computers are bad at replicating the "friction" of war.
The other factor is the expense of equipping a soldier - in inflation constant 2010 dollars, is cost about $1500 to equip a WWII infantryman. Today's cost is about $15,000 because we want to put night vision, body armor, and communications in the hands of every infantryman in order to maintain absolute superiority over any possible opponent, which saves as many lives of our fellow citizens as possible (competent commanders being the other great life saver). I can train an infantryman in 30 days, but I can't train platoon leaders, company commanders, and battalion commanders that are really good, without a year for a platoon leader, a couple of years for a company commander, and a good four years minimum for a battalion commander. Bad company and battalion commanders caused a good bit of our loss in WWII.