Hi, from Essex as well. EM tuning do quite a few lighting upgrades, leds for the interior lights and brighter and whiter front Xenon/fog/drl/side lights, all are straightforward bulb changes, so easy to do. I'm not into body and suspension upgrades myself as the Avant looks perfect as it is in my eyes.
There is a 'Cheap upgrade thread' somewhere here, so maybe some more ideas you may like.