I used to have RAC come out and do a roadside repair, but this is considered a temp repair as you really want a "vulcan" repair (I think thats what it is called) as this is where the patch is bonded from the inside of the tyre.
As for doing it or not, I have often got mine repaired and have ridden at ZR required speeds on private roads blah blah.
Once I took a tyre into Essential rubber as I had two repairs already and had just punctured it with a nice screw near to the edge....while sitting there a DR got chatting to me and asked what I was in for etc and explained I needed new boots and why and he laughed at me. He then stood up and pointed at the tyre that had just come off his bike and said "count em"
I made out 14 patches and while I was counting he just added "....and I don't hang about..."
So its up to you. Like wearing leathers a lot of people will scream that you will be killed if you don't wear them, you will also find a bunch of people (like myself who apart from a tiny patch of road rash from a 65mph off in jeans!) will tell you that you can sometimes make your own choice....and thats the key..you need to decide how much of a risk you are willing to take here.
Personally as it is outside of the middle third of the rear and not half worn, its still winter so you will not be leaning over much I would patch it and then consider saving for new boots in the spring