Londinium R24

Your Linea Mini is great for multiple drinks and repeatability. So I would suggest first improve the grinder.
Consider one "titan" flat: the basement seems to be an well-aligned flat with at least 50mm burrs. E.g. Baratza Vario with "alicorn modifications" (search home-barista.com if unaware). From there the sky's the limit from there up to uber flats like Monolith Flat Max with Shuriken burrs or Weber EG-1
AND
one "titan" conical: the basement seem to require well-aligned 64mm conical (if electric). If willing to hand grinder then Kinu M47 is great. If you want to go "all in" for espresso titan hand grinder: Helor 106 with Mazzer 0186c burr [same burrs as in Robur single phase and Monolith Conical v3 and v4 (v4 and addition feed burr] or used HG-1 or new HG-2.

If OP likes workflow of their Mazzer Mini (and assuming its doser is still attached) but wants better in-the-cup capability and range, then I'd suggest Mazzer Major with SSP Red Speed high uniformity (if drinking mainly medium to dark roast espresso and sometimes brew coffee) or SSP Silver Knight low uniformity (if drinking mainly light roast espresso and more often drink brew). But as you know, Mazzer Major was not designed for single dosing. That being said, I have not used any current Mazzer the the "V" electronic and updated upper burr carrier to see if single dosing with these are more tolerable.

And if want to occasionally scratch "the manual lever (no spring) shot" then get a Robot or Flair 58. If you like how that scratch feels and always want to scratch then sell the Robot/Flair 58 and get a Streitman CT-2 new (or original used). Original poster did mention they rarely drink espresso milk drinks (so Cremina steamer less useful). And Cremina (not Streitman) has trouble with lungo brew ratios and larger (>2.5fl ounce) espresso brews due to smaller brew piston. Also original poster listed location in profile is not far above sea level so Streitman open boiler will not be issue.

Disclosure / my philosophy of use:
* Helor 106 with Mazzer 0186c and Mazzer Major with SSP Red Speed burrs (daily espresso grinder is Helor 106). Major is drip grinder and espresso grinder when I play barista at holiday parties.
* Robot barista and Quickmill Alexia with PID (the later is mainly used as milk steamer for guests )
* My preferred espresso beans are medium to medium dark roast. Once a quarter, I brew a quality (and expensive for me) light-roast brew roast as espresso; the bulk of these beans goes to wife for her drip.
* I never drink espresso adulterated including never with milk and typical 2-4 double espressos per day.
* I like challenges: since 2015 to Easter 2021 I have used a Cremina as the sole espresso brewer when I play barista at holiday parties. This does require cooling regimen and equally important patient guests (in-laws). I mention this as shows Cremina is versatile espresso brewer. I will miss the Cremina (gifted away). I also realize this is far from norm and far-far more efficient levers exist for multiple consecutive espresso preparation (e.g. spring lever with large boiler such Londinium or quality-vintage like Faema Lambro/President).

A nice and versatile setup in my imagination would be a plumbed Linea Mini with a Cremina next to it.

Or

A londiniumR24 (if no plumbing possible) or a Londinium Compressa.

My argument against the GS3 for my own personal use is that it's just too much machine for me as the lone coffee drinker in the house. I really value the support network of La Marzocco but maybe the flexibility of the Londinium could make it a winner if I'm determined to go with a lever.

Don't know much about the Londinium. Is it a much better unit than the cremina?

Depends on who you ask. Londinium's temperature is very stable because it's a thermosiphon machine, whereas the Cremina will overheat after a few shots and requires some time (or using a cold portafilter) to stabilize. The Cremina is a manual lever, so you are in charge of the pressure profile. The Londinium has a spring that keeps pressure consistent every time.

The Cremina is also much much smaller, so if counter-space is an issue, it's an easy pick.

Dr G wrote:Don't know much about the Londinium. Is it a much better unit than the cremina?

BTW - great username

Likewise! Love your username.

I'm thinking of just getting my LMLM moded with the pressure profiler (from the coffeemachinist) and getting the cremina as a small unit to master. There needs to be another leap in coffee machines bc current ones are just doing the same tricks again and again....

I've been thinking something similar. I'm coming from the Cremina but a modded LM would be a great companion.

Do you think the smart profiler adds much to the cremina?

Yeah, your grinder is what's really your limiting factor at the moment, I think. Upgrade that all the way and see how things go. Then you might see more about what a different espresso machine can get you. I've ordered a Weber Key, myself, but I think a big flat is probably where you'll end up eventually. Lots of good grinder choices now, just difficult to actually get.