There's nothing wrong with being careful with your expenditure. If you can't realise where the extra value is for the extra cost then it's normal to be sceptical about it (and probably good from a company point of view too). That said if colleagues are doing it then you can do the same with a clear conscience.
By way of a slightly related tale, a company based over on the US west coast I used to work for started allowing people to book "Economy Plus" tickets for long trips. Unfortunately this was based on the US idea of an economy plus service, which is to say a standard economy service with a bit of extra leg room that can be had for buttons on airlines such as United. People took this to mean they could book Premium Economy on airlines like Virgin or BA, where there is a step change in the class of travel and a corresponding step change in the cost of the ticket. Needless to say, the company put a stop to it pretty sharpish.