Other than the obvious difference in price, is it worth it to pay for 1st class for this trip? What are the real benefits over 2nd?

The seats are more comfortable and you get a nice, but not outstanding meal, included in the price plus free drinks.
Whether it's worth it or not is a value judgment; I think it is.

Hi JM,

If you do a text search, you will find several threads offering different viewpoints.

The trip is now only 2.5 hours with the opening of the high speed British trackage. Some of the second class cars arrive a few seconds earlier in Paris and several of them arrive a few seconds later.

If you are on business and your company is paying for it, then it's worth it I suppose. For the every day traveller, for 2.5 hours, it seems to me an extra $100 or more is totally ludicrous.

The "real benefits" are the same as with any other 1st/2nd Class comparison. First class will be roomier, nicer, more comfortable and in this case include a meal. No one can tell someone else if this should be worth it to him.

Thank you for your thoughts. I guess to be more specific...are the seats in 2nd UNcomfortable? Something like not enough legroom or elbowroom?

The second-class seats seem perfectly comfortable to me, but i have no idea how much leg-room or elbow-room you need. The seats are very similar to those on TGVs and other modern trains and are quite big enough for anyone of average European size.

I always go first class (leisure category) unless absolutely unavoidable.
By the way, you can save money by booking your ticket online. But do NOT give the U.S. as your country of residence when you first log on to the www.eurostar.com web site. Pick the UK--you can use your London hotel's address as your UK address--the address you provide to buy your ticket does not have to be your credit card billing address. Arrange to pick up the ticket at the Eurostar ticket counter at Waterloo Station.
Yes, the seats are more comfortable in First. The whole experience is a lot more pleasant, IMHO, and worth the $$ difference.
If you go second class and you want a window seat, do not accept a ticket with a seat assignment of 22 or 52. Those seats don't have windows, just a wall of the train (although the Eurostar London/Paris trip is not all that scenic).