Ive had a go a couple of times in PP. Im the same i couldn't buy a film camera and get it processed but if you manage to get some good shots on a DSLR you can do a few tweaks in PS to give a lomo look! You can even add light burns in as well as most of the old Lomo cameras leaked light to a massive extent!
I usually equip something like a 35mm f1.8 and take some really detailed RAW shots then you have so much freedom, but by just playing with the satuation and contrast you can get a lomo look and it's easy to add a vignette as well, have a look online for tutorials?