Do you mean you have passed level 2 & 3 as level 1 is no longer offered?
I have studied to level 3 and currently studying for the Self Assessment module and will be studying payroll next. I bought all the 3 levels core courses as a package from kaplan, so I guess I will have to do the level 4 exam sometime if I don't want my money wasted.
The reason I haven't prioritised level 4 is I have met many Associate successful bookkeepers who have more than enough work they have had to employ others to help. I have worked for an associate bookkeeper who employed 3 staff. This means that eventhough passing level 4 will obviously enable one to offer more services, you could earn a decent living as an associate. So for me personally, level 4 will have to wait while I tackle the optional courses first. I am yet to get a good answer to the question 'How good will I be to a sole trader if I can't do their self assessment Tax Return?'