On any long distance journey, First Class is definitely worth some money. The seats are much bigger and much more comfortable, and you have regular seat side service. Also, because First Class tends to be less full, you usually have a decent chance of scoring four pax's worth of table unless you are travelling at a really busy time like into London towards the end of a Friday afternoon - and even then you can reasonably often get a table for two to yourself. This allows you to get on with some work, or some comfort in which to read a paper.

How much extra all that is worth does depend on what you're doing.