Visiting Liechtenstein is no big deal - no better than the surrounding bits of Switzerland and Austria, and in my opinion not nearly as good as several other areas in Switzerland and Austria.
But - you can check off a small country on your list.
I wanted to do that myself several years ago, and was seriously under impressed. We hunted for a place to eat and wound up at a McDonalds in Vaduz, a small town that did nothing for me.
The white lettering on black numberplates on cars is kind of cool.
You need a Vignette to drive on any green signed roads (motorways and expressways) in Switzerland and Liechtenstein which will cost you CHF 40 (around €40, but varies based on the exchange rate, available at the border or filling stations before you cross) for the year. There are no shorter periods available. It is the same price if you are there a few hours or a calendar year.
You also need a Vignette for Austria, available at filling stations before the border. Austrian vignettes are available for as little as 10 days, for just under €10, from official filling stations before you cross the border. Look for very large signs with a picture of a vignette, and the words "Vignette Hier" on it.
Both need to be affixed like a decal, by peeling off a layer and pressing the vignette to the windscreen in the way printed on the back of the vignette, in the place indicated. Once applied they are destroyed if an attempt is made to remove it, and it is punishable with a large fine to affix them and try to use tape to hold it up.
The route through Austria between Liechtenstein and Innsbruck has several very long tunnels, especially the Arlberg Tunnel (14 kilometres), all of which cost a toll in addition to the Vignette.