How long is the flight, and when will you be expected to work? If you have a recovery day built into you schedule it might not make much difference.
I find that WT+ *does* make a significant difference to my journey. I find the seat more comfortable and I can sleep better - especially if I bag a front row, and I feel better the next day. Since most of my clients only pay WT I often pay (out of my own pocket) for an airport upgrade.
One of the biggest advantages is being able to upgrade using Avios to CW if there's availability. Since I earn almost all of my miles for flying through work, I have no issue spending them to upgrade work trips to make things more comfortable. I just wish I flew routes that offered these upgrades more!