forget the tube rolling, the preamp is killer in stock form. Try a 14" bike inner tube under it to see if you like the sound if not then try some points.
Yes I would agree with Bigkidz about isolating the LA150 with some sort of points...either a sistrum rack or walker valid points. I have tried both and they do make a nice improvement.
I would also highly recommend an upgraded power cord. I have use a number of them with varying results. I am partial to electraglide products but also had good luck with Silent Source which are moderately priced and marketed by Walker audio. Power cords and IC's are so system and ear dependent that the best advice I can offer is trust your ears to get the combination that sounds best to you.
As far as tube rolling is concerned, Jud Barber already uses NOS tubes in the unit so that is not an area that you can improve on really.
I love the LA150 and have it mated up with a Joule 80-80 which is a dynamite combo.
If you need any other help, email me off line and I will be glad to provide any help that I can.
Use an isolation platform that has air in it. In addition I use cones from black diamond. As far as power cords go the Joule loves "FAT MAN" from Electraglide. As for tubes, you'll have to spend a LOT of money to buy better tube than Jud uses from the factory. Although the 100 and the 150 pre amps work well with almost all high quality power amps you must hear them with one of the amps from Joule Electra. Enjoy
No it is not a giant killer but a very well balanced performer. The CAT offers a similiar sound and the CJ is a step up in the mid range, a little sweeter and I forget what else. The Tom Evans SS preamp is what you are looking for if you want a great preamp for the price (used price). It was the most natural preamp I have heard to date. All info is MO.