I feel the Arya is a significant step.
My second "real" headphones were the he400i, I loved those things back then. When I had gotten the Sundara I A/B tested them and that proved to me that there was no reason for me to keep using the 400i, it was just a noticeable improvement. I feel the same for the Arya, the bass is night and day as well as the soundstage. Detail seems to be easier to notice and I don't find them as bright sounding overall as the Sundara.
I got the Arya roughly 2 weeks after the LCD-4 and the Arya still only impressed me.
I would dig around a bit, I managed to get the Arya very lightly used for $1400 CAD.
At that price I see the Arya as the best bang for the buck, even compared with Sundara before who I gave the nod of best bang of the buck towards.
Now I know everyone will have varying tastes, but I believe that if you do enjoy the Sundara and the music you are listening to, as well as traits you are looking for, that it would be quite surprising if you didn't appreciate the difference and not have regret "besides your bank account that is!"
I imagine they would be an easy sell if you did feel the money was too much for not a big enough jump, as yes it is a lot of money for headphones at the end of the day.
Thanks for the lengthy and judicious reply; it was of significant help.
I found a good deal on a new pair of Arya's (no open box, no B stock) that I could live with from a reputable official hifiman seller so I went ahead and got them. With all that's going on shipping might be a mess, but they should be in here in a 2 weeks tops. I'll do some lengthy listening/getting used to them before I post my impressions. I just hope my Gilmore Lite Mk2 can drive them well or else a RME ADI 2 DAC might be in my future (love the way that thing looks for one), but hopefully not for my wallet's sake!
Two main things drove my final decision:
I sat today and really listened to the Sundara's with a lot of different music of varying sound quality, and while at their best with the most well produced tracks they sounded great and I'd be pretty happy with them (at least for the time being; my T1's are better cans, but I loaned them to an out-of-town friend a few months ago and with all that's going on, including his recent job furlough, I said he could keep them indefinitely), even when they sounded their best I can tell something is lacking. Some lack of clarity, openness, "scale", and some "glare" or hardness to the upper mids and highs, and also some lack of refinement or delicacy, especially in the highs. Also, while I find their sound stage adequate for most all genres, I could use a larger one, even on rock/pop/metal. With these you ultimately feel like you are listening to a headphone. That intimacy can be good, but I do like a more immersive sound stage, at least if it doesn't become too unfocused.
And also the cups just aren't the most comfortable on my ears for extended listening. It's not a "can't take it" level of discomfort, but it does detract from the enjoyment of the music, especially after a couple of hours. The cups are just too shallow...and my ears are medium sized and don't stick out far from my head. (Yes, I know I can buy different pads for a lot less than new Arya's, but I'd rather just take the leap to ultra-comfortable headphones instead of sinking $50 to $100 or whatever into new pads.)
That, coupled with the discount I could get if I acted fast, along with the knowing that waiting for perhaps a really good deal on new Arya's in the coming months would nag at me (what am I missing right now?!) propelled my decision. I just hope I find that they are worth the price, but I know that where others find only marginal improvements between lower and higher priced gear, I generally find significant ones (often the differences are subtle, but as with many things in life, it is the subtle contrasts and qualities that really count).
I went from Sundara to Ananda to Arya and it was worth each step up along the way for me.
This helped as well, thanks.