Hi Maz,
I've just returned from Cala Llonga, having been going there every year for the past 23 years (I have a timeshare there in the apartment block beyond the Playa Imperial hotel)
Needless to say I'm biased regarding the resort, but would be the first to admit that it's not the place to go if you want lively nightlife. However, as you say you want it relatively quiet, you have chosen the perfect resort.
I agree with everthing "allmen" has said regarding the resort, especially the beautiful and safe beach. The Wild Asparagus is indeed an excellent restaurant, and the pleasant walk back to the village afterwards is an ideal way to walk off an excellent meal.
However, there are several other excellent places to eat in Cala Llonga, and loads more to be found in Santa Eulalia, which is only 10 minutes away on the hourly bus service and costs just over 1 Euro. Returning at night by taxi, (the last bus back is at 8:30pm) will cost about 7 Euros.
Best places to eat in the village are Zebra Restaurant (my own favourite), Vela Blue and the Cala Llonga Restaurant which is situated on the beachfront and has an open grill which is worth a try.
As for bars, it all depends what you are looking for. Mr. Cairo is popular with Brits and does pints for 2 Euros until 9:00pm, after which it pretty much doubles in price. The Blues Cafe and Raffles are the only two bars open really late (around 4:00am) and I personally much prefer Blues Cafe. Madison is ideal for watching the World Cup as Pepe has about 200 seats placed outside and has 4 good sized screens. La Cantina is British owned and run, in spite of the name, and is a friendly pub.
If you tell me where you are staying, and what sort of nightlife you are looking for, I'll be glad to give you as much advice as you want. At the end of the day however, it's a small resort and you might just prefer to try each place and weigh them all up by personal experience.
Hope you have a great time anyway.
JJ.