I have both.
A big thing in SoCal is how long would things stay cool in case of power outage. My offsite is like an old fashioned ice house, and with all the cold mass in the well insulated room, I’d bet it would be ok for a week if no one goes in or out. At home, maybe a day.
With a sufficiently large storm in a low-lying area, even off-site facilities are at casualty and associated financial risks. The key is a special insurance rider to cover regardless of location.
Also have both. I filled up my on site cellar in about 3 years. My off site is also getting filled faster as I find I am less selective when I have open space to fill.
As a south bay resident, I definitely feel this and I’m also curious about why, though I definitely have an idea and it’s something along the lines of… Rombauer swilling and cases of the latest blown out napa cabs kept under the bar at home and drunk in relatively short order. Not exactly a bastion of nerdy and/or AFWE folks around from what I can tell.
There’s a guy witha walk in at my storage facility in Pasadena that’s just filled with Steakhouse Napa Cabs
I currently have wine at two facilities and have definitely been shocked at seeing what people pay to keep in there…
To answer my slightly younger self (and for anyone else who is looking for input):
I’m happy keeping bottles that I’ll open within a year at home in my wine fridge and bottles that I want to lay down for 1 or more years offsite. My offsite doesn’t accept shipments, but I ship my wine to my office.
Also, my storage facility is cheap enough that I wouldn’t feel bad storing anything I like in there, even if it’s just steakhouse Napa cabs 
(even though that’s not what’s really currently in there).
I own a non-wine self storage business that has some parking for RV’s, trailers, etc. One of our tenants is paying middle double digits every month for a Ford Grenada with two flat tires and plates that expired two years ago. Kaching! Then there’s the wooden boat with missing planks on the sides of the hull and a ‘for sale’ sign. It’s been there for over two years.
And, that’s why self storage cap rates stay strong. America has a lot of crap and needs somewhere to put it!
I’ll be curious how much longer this is true. The amount of institutional money pouring into storage, and the number of very sophisticated investment managers channeling that money, is truly staggering (well, staggering to those who think of ‘real estate’ as an office, a mall/strip center, or a warehouse). You use the term ‘cap rate’ so it’s probably not a surprise to you…
One observation to OP - make sure you like the taste of your collectible categories after they have some bottle age. When I was much younger I laid down some vintage bubbly. Over the years I felt like I always preferred it before it developed the aged nutty flavors. So now I keep limited amounts around and just buy & drink it as needed.
Also consider what should get cellar slots if your storage is limited. Some types of wine are pretty easy to find years later, others are not. I’d suggest saving your own storage spots for the ones that would be much harder to find in the open market later on.
Enjoy the journey!
Can anyone recommend off site in the south Florida area?