My short answer is depends what you want to do.
The long answer is more like:
For massive track bashing sessions a long way from home, and spread across the UK, then yes absolutely!
For a lot of long-haul journeys on East Coast, Virgin, FGW etc then yes absolutely!
For a tour of the UK, with a set-in-stone plan and no rush to get there or change plans at the drop of a hat, less so, but would depend on the journeys being made.
That's my basic reply, I could go into detail but I'm on my phone on the way home. As I suggest above, an ALR is well worth it depending what you want to do.
I've done both a 7 and 14 day ALR in 2011 and 2012 respectively, and loved each minute of it, not wanting the trips to end and they went by so fast it was unreal. These days, as my track requirements in the UK are almost exclusively PSUL moves, preserved and non-passenger lines, an ALR represents less value. However, I almost did one recently (see my "I've got a dilemma" thread) again for the long distance stuff. If I hadn't already committed money to some Advances and cashed in my East Coast Rewards ticket, I would have done one. Of course, I didn't (see "Techniquest's Sticky Digits Chasing (Trip Reports)" thread for what I did do) but I still wonder what I would have done, where I would have gone and if it would have been better.
I'm still hoping to do another ALR in a couple of years time, but that'll be enjoying the last of HSTs on the Western Region/ECML and so on. Still very much TBC of course...
Whether I've helped make a decision or not I don't know, but if you're not sure about doing one you don't want to do it!