While 'too many cooks' got my vote, I'd also suggest "Designed by Committee" which is us usually used as an insult. If the 'too many cooks' seemed a bit trite or homespun, this newer spin might be called on.
- Note - this phrase is not nearly so applicable to personal advice without some extra careful context building - yet, if it were your vacation itinerary or some sort of costume for a party perhaps it could also work on a personal thing like that.
Like idioms, for it's point to be made it needs to be used correctly to signal it's idiomatic meaning and the audience needs to be aware of the idiomatic use.
I think american professionals are well acquainted with the term but not sure if it works in wider circles.
Design by Committee at the Wikipedia
Design by committee is a disparaging term for a project that has many designers involved but no unifying plan or vision.
The term is used to refer to suboptimal traits that such a process may produce as a result of having to compromise between the requirements and viewpoints of the participants, particularly in the presence of poor leadership or poor technical knowledge, such as needless complexity, internal inconsistency, logical flaws, banality, and the lack of a unifying vision. This democratic design process is in contrast to autocratic design, or design by dictator, where the project leader decides on the design. The difference is that in an autocratic style, members of the organizations are not included and the final outcome is the responsibility of the leader.
The term is especially common in technical parlance; it legitimizes the need and general acceptance of a unique systems architect and stresses the need for technical quality over political feasibility.
a camel is a horse designed by a committee