Just got back- it was Faaaaab!
Arrived Saturday night (leaving 24deg and bright sun in the UK, arriving to very low cloud, nil visibility and 12 deg in Keflavik, mind!, so saw very little of the famous lava landscape driving to Reykjavik....) - but the next day dawned much better- note how I used the word 'dawned', re the sun -it didn't dawn as it never set, really! No actual darkness at all. Weird.
Morning on a local sight seeing tour which was interesting, afternoon at the above mentioned Blue Lagoon. Fab, fab, fab. It was great but what I liked was a) how clean it all was and b) how relaxed the employees were, no tooting whistles or excessive rules. Got a real good look at those lava fields, too, on the drive down. You need to see it to believe it.
Tapas for dinner. 8 dishes (not that hungry!) plus bread, plus 2 beers, £28.
Monday, Golden circle plus super jeep trip up to the ice cap to snowmobile. Spent the entire day out with a guide (8 of us) bouncing along the lava roads. A real highlight. DH and I thought we'd be a bit 'ho hum' having between us seen Niagara, Victoria and Iguazu Falls before seeing Gullfoss; and ditto Geysir after several trip to NZ, but both were absolutely fab. Then up to the Langjokull glacier- bright sun, glistening ice, me making an idiot of myself by being last on the snow mobile 
. Burgers for dinner down in the main square of Reykjavik (famed, apparently), and a walk along the water front to admire the scenery, mainly the mountain Esja overlooking the capital.
Tues- satisfying a long held desire of mine to go to Heimay in the Westermann Islands as I can so remember when their volcano, Helgafell, suddenly exploded and formed a new volcano in 1973, grainy probably b&w night time footage of the islanders being evacuated as the mountain spewed lava and ash! Loong day, fascinating landscape, Eyjafjallajokull (that volcano!) dominating the landward skyline, very blowy and a bit cold, DS2 rather seasick on the birdwatching boat trip (puffin central) where we all got drenched- day made rather longer by our guide, once we'd returned to the mainland- realising he'd left the van key in Heimay, a 30 minute one way ferry trip behind..... So had to wait for the service bus that stopped at every petrol station on the 70 odd miles between the ferry stop at Bakka and Reykjavik, but heigh ho! Takeaway pizza for dinner as we had a 4.45am get up to catch the 2 hr 40 min flight home today!
You're right re expense, though tbh, not as eyewatering as we'd thought. OK, the whole 4 nights, 5 days (arrive one late afternoon, leave last day at 'dawn', all the tours and BL entry fee, transfers and a 3 bedroom apartment with kitchen at the Hotel Fron on the main drag (at the back! The main drag is party central at w/ends!) came to £3200 for a family of 4 (with a 12 yr old) inc flights and parking at Gatwick.
Big (440ml) cans of Viking beer were £1 each, bottled beer like Mexican was £1.80 in the tapas bar, 12" take out pizzas were £5 each. £3.99 Asda stylee wine was £6.50 a bottle, so not gaspingly expensive at 200Kr. to the £1.
The highlight of Iceland is the scenery. They call 10 trees standing together 'a forest' - vast swathes of it are contorted lava, dotted with wild blue lupins and the older stuff covered in pale green, thick moss. It is utterly 'other-wordly'. The skyline is a line of snow, the glaciers, the valleys in many places are dotted with wisps of steam rising up from thermal vents. Vast skies. A geographer's wet dream, as my DH said...
Crazy. But you must all go and I shall charter a Mumsnet plane forthwith!