I reckon 2 sets of tyres are the way to go, if you keep an eye out you can normally get some second hand rims and tyres at a really good price. I have a second set of tyres for the mud, BFGs, they have gone really well everywhere i have gone so far...(hey kent i dont even think ive been stuck yet!except for that time when i gt stuck trying to pull you out at thompsons

) maybe i stick to much to the easy stuff.....anyway, yea two sets is the way to go, then you get the best of both worlds.
Also before you go replacing your leafs, you might want to consider getting them re-set, i have re-set leafs in my landcruiser, and it sits quite high(nothing extreme but it does the job).Pics in photo album Fearce, page 4 of the user pics. Unless of course they are really shot like, rusted away and all krappy, then i guess you gotta.
Depends how bigger your tyres are you buy as to how much more hieght your tyres give you:)
Hiluxs have the leaf set to the axle on top dont they?unlike others that have the leaf spring connected to the bottom of the axle?am i right?which makes em sit naturally a bit higher.
Creepy crawlers sound gooooood:)
Oh and welcome to the 4wd community......aren't we nice blokes??
Sam