Two very different things argue against this kind of attack.
One is the AID that a country like Switzerland is to a warring Power. The Swiss could, and did, maintain economic ties with ALL the engaged states during WW II. This was a place that Germany could get hard currency from throughout the war. The Swiss maintained trade with the Reich, including these little things called ball bearing, throughout the war. This provided Germany with a source for ball bearings, as well as many other products while internal German sources were getting the pougies bombed out of them. At the same time, the Swiss were actively trading with the Western allies, including the licensing of newly developed andvanced manufacturing techniques for... (wait for it)... ball bearings. Neutrality can be a very good (and profitable) thing for both the neutral AND the combatant.
The second reason that invading Switzerland was very unlikely is the Return on Investment. The Swiss have, over the course of centuries, created a hedgehog of a country. The terrain is wonderfully suited for defense, the people are fiercely independent, the national militia is what the U.S. Founding Fathers had in mind when they crafted the 2nd Amendment, and it is possible for a small number of defenders to hold the primary access points into the country against a much larger force. The invader would have to largely destroy the country to counquer it, eliminating the reasons for invading in the first place.
German troops would, in all likelyhood, have won out (although the Wermacht's Yugoslavian experience makes this far from a sure best), but at what cost? Is Switzerland worth four or five shattered divisions, especially when you are planning (or at least resigned) to fight a two front war? I would point out that the Germans had more troops tied down in the Balkans fighting insurgents in the mountains than they, at one point, had facing the Western allies in France post D-Day.
In all Switzerland simply wasn't worth the trouble. That was, and still is, the Swiss international strategy. Trade with anyone, treat everyone the same, and be ready to imitate a blowfish if the need arises.
Its a plan that's worked for the better part of the last THOUSAND YEARS; it must has SOME validity.