Sending a probe to Alpha Centauri - is it worth it?

Every once in a while the idea comes up to send a probe to a nearby star, using a huge amount of propulsion in a journey that takes about 50 - 100 years. One of these is Project Daedalus, a probe to go to Barnard's Star, a very nearby red dwarf star (5.9 LY) that at the time (the 1970s) was thought to have a planet.

Another one from the 1980s is called Project Longshot, and would be a probe that would go to the even closer Alpha Centauri system. On the Wikipedia page there's a scanned pdf from the mission proposal, and because the image quality is not that good I'm thinking of typing it up to make the content searchable for others to reference later on.

Since we're just about at the point where we'll be able to tell what planets exist around Alpha Centauri there's no reason to go for a project like this at the present, but I think the debate will come up again pretty soon if we are able to find an Earth-sized planet around one or both of the stars.

One point often brought up on the forums at space.com though is that with the increase in astronomical technology over time, wouldn't we be able to obtain better observations of these stars over time just by staying put and sending out better and better telescopes all the time? 50 years is a very long time, and a mere 20 years ago we didn't even have the Hubble, nor had we ever seen Neptune up close. So that's hard to say. I was thinking about perhaps a two-pronged approach, one probe made to be as light as possible to get there in the quickest time we can, and another one with more mass to give it its own powerful telescope. When probe A has gone 80% of the distance for example, probe B will have gone perhaps 60% of the way, and perhaps even after the decades had passed would be able to provide better observations of the system than we could get back here. And just in case it could also be used as another Kepler-type observatory, to take long exposures of stars and look for other planets on the way, something like that.

I'll have to take a closer look at the document as I type it up though. If the engine is to be on the whole time it wouldn't be possible to make any observations on the way during that time.