Others experience re: subs and Magmepan 20

"....My question is .... but rather other folks experiences who have tried this and do they feel they got substantial benefit from an extra half octave added to (almost) full range speakers to justify the expense, hassle and real estate taken up in the music room..."

In short....you betcha....a big-time audio performance improvement BUT only if done "right" as highlighted in the reposted article.

I have seen and heard too many subwoofers introduced that simply bloat , muddy, chuff and destroy the audio reproduction simply because they were a crap and  crummy match to the 2-channel speakers primarily because they were indeed cheaply built kit .... full stop.

To CLEEDS
"....
There is no one subwoofer, there is no one component, that is perfect in every system. The world of audio just isn’t that simple...."

I never said it was the final single bests-all-comers solution ..... it wasn’t my article ...just a link to a third party article with a quality background read highlighting on the strengths and warts of ALL subwoofers, ( note the article title ) that also happened to include that writers suggested fave in closing that you can reject if you want to.

I know, you know, we ALL know that there is no one-size fits all to perfection choice, to quote your metaphor.

The Vandy is a very very fine contender AT ITS PRICEPOINT in a large arena of pretenders ,

BUt

I would gladly upgrade further to, say .... an ATC C-1 subwoofer that starts out north of $10,000 and goes  up,(if I could afford it) as just one simple example.

OP, at what freq. is the 20R 3 db down?

and what music do you listen to that has much energy at or below that freq.?

@imdoc , I think you are crossing over too low and the 3rd order crossover (correct me if I'm wrong) is a bit extreme. I would use something less drastic, like a 1st order crossover (-6db) starting at 70-80hz. If you have a well made powered sub, it should integrate and provide you with the bass you are looking for.
Not to beat a dead horse, that is why the Vandersteen crossover and subs do so well in terms of integration.
@akg_ca , If I, or 98% of the Audiogon readers could afford a $10K sub, then, yes, it might make a difference, but considering the OP has a pair of not quite current Maggies (and I wish I had 'em), I doubt he/she would entertain a pair of ATC C1's.
For comparison, I have an office system with a pair of Hsu VTF-1's paired with Zu Omen bookshelves. The Hsu, in no way compete with a pair of Vandy subs (which I used with a pair of Zu Union). I was blown away when I played music on them with my Atma's. So, using your Janis subs would kind of be like using my Hsu's, but YMMV.
B

"My question is less about what equipment and integration issues (that would a whole, complicated discussion alone) but rather other folks experiences who have tried this and do they feel they got substantial benefit from an extra half octave added to (almost) full range speakers to justify the expense, hassle and real estate taken up in the music room."

You can't separate the two. If you put 2 different solutions in your system that both get that extra half octive, they can sound completely different. It's a matter of quality and system matching. Just getting the system to play lower notes won't cut it in your system. I'm not a huge fan of Magnepan, but if there's one thing they do well, its bass. They take the quality over quantity path, and it sounds great. The only downside is that it's harder to integrate a sub.