How necessary is a 1 degree spot meter for 35mm & MF shooting?

I use a spot meter for all my large format stuff, but I just use the built in meter on my F5 for all my 35mm stuff - it works fine (I shoot only transparencies in 35mm).

I picked up a 7.5/15.0 degree spotmeter attachment for the Luna Pros for $20.00 on eBay.
It came with a nice black leather case. You can find good analog Soligor 1.0 degree meters fairly easily also. You can ad a Zone scale to the barrel for $3.00. And what's really good news, you can get on a waiting list for a genuine Zone VI Modified Digital Pentax Spotmeter. The wait is about 6 months but who couldn't put aside $20.00 a month for half a year? Contrary to rumors, Pentax is still building their famous spotmeters but can't keep up with demand. If you're going to REALLY implement the Zone System (or the variants thereof), you should use a 1.0 degree spotmeter.

All depends on what you're trying to accomplish. I seldom carry any kind of meter for my folders, and use whatever's built in when I use a camera that has one (and none of them are one degree). I only routinely carry a meter when using my plate cameras, and that's a Gossen Sixtomat that was used when I bought it, near enough to 35 years ago; definitely NOT one degree (more like sixty!). I'm pretty happy with my images, overall; my eyeball exposures routinely produce negatives that print easily and well (now that I'm able to print them, I can make that statement!).

An incident meter handles most situations quite well, and for most motives the camera meter works fine too. After a while you will learn to see how light is distributed in the motif and then you will learn how to meter and how much to compensate. If you use a camerameter I would suggest using it in one of the simple modes such as "average" or "x% center". The reason is simply to learn how to correct the readings yourself, and not let the camera try to understand how the motif is. Afterall your brain is a lot smarter than the meter.

I don't see why a spotmeter is more important for LF than MF or SF, except that smaller format cameras often have fairly good built-in meters (at least the "new" ones).

I must admit though that I have a spotmeter myself and that it can be handy in some difficult situations. Typical situations are high-contrast motifs and motifs where powerful lightsources are directed towards you (the sun, backlit scene). My meter has incident, 5 degree and 1 degree spot. One of the useful things about it is that I can measure motifcontrast - for those purposes 1 degree spot is really great and you learn a lot about how light is distributed in a motif. It can also be nice when you're using films such as Agfa Scala ... if you first block the shadows.. which can be done by underexposing only one stop.. argh! (but the perfect exposure... mmm!)

Another recommendation is to only use the one separate meter if you have one. The reason is simply that different cameras have different meters and different ways to "understand" a motif. Also, some meters always underexpose slightly, som always overexpose etc. So, why not use one meter to rule them all!

Anyways.. I don't find it difficult to expose correctly. It may of course have something to do that in my first two years with a camera I only used a rangefinder with a builtin average meter and that it forced me to learn.