You are going to get both yes and no responses. Some people think upgrading is a good idea and others think it is a waste of money.
I've taken Virgin trains numerous times and have done the Glasgow to London route. I upgraded to first. I liked it and would do it again. If you are going during the week, you get a meal. If on weekends, a sandwich. Free non-alcoholic drinks and even a case were you can help yourself to bottled water. I also find the seats bigger and more comfortable.
In first class, the seating is 2+1. You could get two individual seats facing each other with a table between the two of you. Or share a table for four.