Politician: Over the next decade, our city will be replacing all of

Over the next decade, our city will be replacing all of its street signs with signs that are designed for improved readability.
But no one is complaining about the current signs

Conclusion: installing the new ones is a colossal waste of time and money.

We need to evaluate the conclusion - whether replacing signs is a huge waste of time and money.

(A) What features of the new street signs improve the readability of the signs?

Irrelevant. We need to know whether it is a waste of time and money.

(B) Are the new street signs considerably more expensive to manufacture than the current street signs were?

Irrelevant. Cost of current street signs has no bearing on whether new signs are a waste of time and money. The current signs could have been manufactured decades ago and might be much cheaper. If we do compare costs, then it makes sense to compare current cost of manufacturing the same street signs (which are used while replacing these as part of annual maintenance) with the cost of manufacturing these "more readable" signs.

(C) What percentage of its street signs does the city replace annually in the course of ordinary maintenance?

This is relevant.
Say the city NEEDS to replace only 1% of its signs every year (broken or not readable etc). So over a decade, it would have replaced say 10% of its signs. Then it does seem that replacing all signs in a decade is a big time and money commitment.
Instead, say the city NEEDS to replace about 10% of its signs every year. Then over a decade, it does end up replacing all signs. Then, if we replace them with the new better readable signs instead, it may not be a waste of time and money. New signs would anyway cost money. More readable signs may cost a bit more but it still may not be a colossal waste of money.

(D) Do any other cities plan to replace their street signs with signs designed for improved readability?

Irrelevant

(E) Were experts consulted when the new street signs were designed?

Irrelevant. We know they are more readable.

Answer (C)