Assuming you don't get concord access you have a choice of better food or the spa, or indeed both if you pins are OK (its only a few minutes.
I think this bit from flyertalk.com sums it up quite succinctly;
At Heathrow T4 there are two sets of lounges. One (by Gate 1 à ÒThe Gate 1 LoungeÓ, it is no longer strictly speaking branded as a Terraces) offers a multi-level Ôbusiness classÕ style-lounge complex. The other, by Gate 10, contains the Concorde Room, Spa, Terraces and the FIRST lounge. If you only have Terraces access and are not bothered seeking a Spa treatment, you may find the Gate 1 Lounge better as it is normally quieter and has an excellent hot food operation called the ChefÕs Theatre not found in the Gate 10 lounge. Of course, if youÕve got enough time you can try both Terraces lounges!