At senior levels a surprisingly large percentage of club secretaries are ex referees, often ex senior referees. Turn up looking like you've got dressed in the dark, or in kit that is more grey than black or one that belongs in the 1990s, and you are risking your club marks before you have even started the game. As an aside, turning up late is pretty much guaranteed to affect your mark with these guys, especially if you have forced them to chase you up. As is over claiming mileage, not joint travelling when you should have, bringing a guest without notice, etc. Any referee who does any of this at level 4 and above is a fool, or must be so good that they can afford to throw away marks.
A lot of the observers are part of the elderly generation, who in their day had to have pristine clean white laces and sock tops, this is even more so at level 4 and county observing levels. How a referee looks on the pitch should of course never, ever affect the overall mark / grade, but anyone that thinks that it doesn't is living in cloud cuckoo land. It probably won't get mentioned in the report, but if you are borderline in a section it might turn that 7.5 into a 7, or a well above standard into above standard.
So you don't absolutely need the latest kit to be a level 4, but at that level you should not be doing it for the money, and for the sake of a couple of match fees my question would be why do you not get the latest kit? As a level 4 who is active most weeks throughout the season you are likely to be bringing in close to £2,500, plus expenses. Surely you can afford £70 out of that ...?!