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"First nuclear weapons are devices. They use precise electronics, which have to have microsecond timing in order to cause detonation. Not something that you can cobble together from that old VCR. They need to be maintained in order to insure that they work when needed."

Most of the electronics in a nuke are unnecessary baggage. As for the required stuff, say, the timer to set off the shaped charge just right to convert the slightly sub-critical mass to a critical mass, that is very simple electronics.

"They require a power source, which means batteries. Ones not available at Radio Shack."

Do you know how much juice it takes to set off the explosives? Just plug it in to the wall. Why do you need batteries? And how do you know that you couldn't get a suitable battery at Radio Shack?

"The triggers (basically switches) which set off the explosives that cause the detonation are gassed, and lose their switching speed over time. After 5 or 6 years, their timing gets off, and they become unusable, due to outgassing."

Old tech. Off the shelf solid state electronics can do the job now.

"Then there is the explosives themselves. They lay against the pit (plutonium core) which is thermally hot, and causes the shaped charges to degrade over time, losing their ability to fire a predictable rate after a time."

So replace them. That's easy.

"All weapons, in order to be safe, have an MSAD built in. You would not want it to go off until you want, right? This requires an external arming device, which is mated to the device (for portable ones)."

There is no way it could go off unless you initiated the (brand new solid state) trigger. This is just more extra junk to prevent theft-and-immediate-use situations. And we aren't talking about portables. In fact, the scenario I see as most likely is a sufficient quantity of Pu239 salvaged from an old warhead is brought into the US and the rest of the nuke is built around it from parts acquired in the US. So we are talking about a slightly sub-critical mass of plutonium, some HE and some relatively inexpensive electronics. We aren't talking about taking an existing device and flipping a switch.

And, finally, plutonium will go critical all by itself in relatively small quantities. You have to be careful not to pile too much plutonium up in one spot because it will go off. For all you people out there who aren't keeping their plutonium piles properly separated, you have been warned.

You did not do so well in chemistry, did you?

The shaped charges, and the timing of the explosion is crucial to successful detonation of the fissile material. Without them, you have a dirty bomb, and not a very powerful one. But that is another thread.
The idea of "harvesting" a pit from somewhere for some home brewed nuke is interesting. Plutonium is not particulary radioactive, but does oxydize readily in the air, and produces a fine powder in dong so that contaminates everything and is easily inhaled. Did I mention that it is EXTREMELY toxic? Once you have the pit, you have to have the mathematics necessary to know how much overpressure needed to fizz the pit, and have the specilized skills necessary to construct the charges. Not exactly something that is taught in the Madrass.
These things cannot be slapped together, and expected to work. General nuclear weapon theory is common. Having the resources to build one is not.

"And, finally, plutonium will go critical all by itself in relatively small quantities. You have to be careful not to pile too much plutonium up in one spot because it will go off." - calenel

Not according to this site:
In order to start the chain reaction, the mass of plutonium must be fused together while a radioactive source emitted a neutron.