Your never going to get that answer. It is too subjective. “Worth it” can never be communicated properly.
The short answer is the MG 20 is more. That is about it. More. How much? Again, no way to communicate it. I will say, to get the the “most” out of them, you need a big room. You don’t have to have a big room, but it will give you “more”.
If you are gun shy, don’t do it. This hobby is not for the timid given the high dollars and commitment of time.
Peace
Bruce in Philly
Bruce, my room is 23.3 X 22 with 8 foot ceiling ( in the center 16’ ) then tapers to 5" side walls
That room, to me, is “goofy”. It can be great or horrible. That ceiling is a demon or angel.
The MG 3.7i is a fabulous speaker and will produce music. I can not see how anyone would be unhappy with them as long as they are given current (not watts), and care during setup (over and over). I they work for you, then upgrade to the 20s.
However, I never heard a Magnepan really rock. For that, you need a traditional cone speaker IMO.
Peace
Bruce in Philly
Only place I heard them was in Evanston Illinois at Audio consultants
The 20.7 - for me - was a knee wobbler. I love soundstage and man do they provide it. If I was going to pick a couple things they do better than the 3.7 - I’d say it’s the bass and mid bass- and it’s all planar bass. The difference for me was: 3.7 that is a really nice sounding speaker - but hmmm do I need a sub? Do the mids have the warmth I like? With the 20 - all those needs are met which creates the complete landscape and everything including the stellar ribbon tweet just fall into place.
My brother heard them first and said - ‘you don’t have to hear these’. He was right. But it would have been difficult to pull the trigger without hearing them for sure - as speakers are a very personal choice.
If you are ever in Ann Arbor Michigan - you are welcome to stop by. 
Whenever I am listening to any of the more expensive Magnepans I am totally loving what I hear and wondering why I have never entertained owning them. It’s odd but I have some sort of mental block about them. But oh do I love the sound.
Let me be clear. I really like my 3.7i pair. I feel they are the most honest sounding speakers I have owned, ever! I just want more of it. I am looking for the Maggie honest sound with more mid bass ( I have a JL Audio F113v2 pair which complete the bottom end amazingly ) and a bit more dynamics.
I don’t regret buying the Maggies at all! Just wanted to be clear. Just looking for the next step up, or should I say two steps up. I did consider the 30.7 as well, but I am not sure my room can handle them.
Has anyone ever made a Maggie type hybrid with cone woofers and mid bass coupler? That would be interesting
That being said, if the AN series was out, I’d be swayed maybe away for the Maggies…?
In a few weeks I’ll be able to hear my friends new speaker. The Dynaudio Confidence 60
Has anyone went from 3.7i with added bass panel pair to 20.7? I have a chance to grab a pair of the DWM bass panels.
I’m curious why you are saying this when in an earlier post you said the dealer was offering full purchase price of the 3.7i towards the 20.
Seems a no-brainer to do the upgrade that way instead of selling to another forum member.
I could still use the bass panels with the 20.7 if I needed to. Just curious. Not looking to spend a bunch of money if I don’t need too.
What do you mean ‘bass panel pair’? Tympani bass panels or their DWM bass panels?
Yes Timm the DWM bass panels
I am considering the 20.7 upgrade and could always use the DWM panels with the 20.7 as well. My room is funny, it sucks mid bass and upper bass like a sponge but has bass nulls around 75 and 60 hz. So if I use my sub at 80 hz on crossover I get too much bass bump. If I use sub at 40hz it’s amazing but I get a lack at say 120-80 hz with my 3.7i. SO I need to raise the upper bass to mid bass hz range without my subs… or I could try to use a DSP module on my subs?
Well the dwms need power - and running them off the same taps decreases impedance which could impact how your amp drives your mains - that’s one problem. The other is the need to have a filter on the high frequencies on the dwm? Then you also have to bring your subs into play. This is sounding complicated. :).
I have my 20s and a ml descent sub essentially pushing frequencies of 25hz and below. Everything above that is all panel. My room is a ‘bass suck’ as well. It’s 17x30 w carpet/pad over cement. Drywall with heavy a acoustic tiles in the ceiling. You walk into it and everything gets real quiet.
Remember - the 20 has dual magnets on the front and back of the panel for mids and bass whereas the 3.7 I believe has single sided magnets. Also the frame on to 20 is more substantial. I think the 20.7 weigh 175 each. That says a bit.
Timm, thank you for helping me with my decision. I’ll look into the 20.7 for sure.
I have the 20.7s and I bet there is no owner of 20.7s that is needing the bass panels. My rel subs are set at the lowest crossover point
I thought you might give your 2 cents Minnesota. Agree w you.
So now my dealer has changed their tune on the trade in policy… So I’ll be selling my MINT black oak, black cloth 3.7i pair if someone is interested. PM me. New in April 2019.
https://forum.psaudio.com/t/magnepan-3-7i/12163?u=darrenv1070