We’re not surprised that the Cumberland County Civic Center board of trustees has come up with some very pointed questions about developer Jason Snyder’s proposal for a new sports arena and downtown convention center.

The trustees have been working on a civic center renovation or replacement plan for a long time, and Snyder’s idea comes late in the process with a lot of rounded-off numbers and not much information about where the money will come from.

For instance, Snyder estimates that it would only cost $60 million to build a state-of-the-art arena, while the trustees’ estimates put the bill closer to $100 million. If they are really talking about the same thing, there needs to be a detailed explanation about why the numbers are so different.

But we are surprised to hear Snyder say that the trustees are hostile to any plan that includes a convention center.

If that’s true, it is disappointing. A convention center could provide a valuable economic development opportunity for the region, and it would be shortsighted not to see the potential public investment in the civic center as an opportunity to expand its usefulness.

Portland is already a popular site for small conventions and affinity group meetings, and not just during the summer.

It  lacks space for larger meetings that could attract bigger organizations.

Unlike a civic center patron, who comes into town for a concert or hockey game – paying only for a ticket and parking but little else –  a convention-goer stays in a hotel, eats in restaurants and may sneak in some shopping in his spare time.

Other cities have found that even if the facilities only break even, they create enough business to be worthwhile.

The trustees are right to ask tough questions of Snyder, or any other developer who has a plan that would involve public investment. The devil is in the details, as board Chairman Neal Pratt said, and Snyder’s proposal so far has been short of them.

But the board should not be sending the message that it is uninterested in any plan with a convention center.

The potential benefits of such a facility make this something that should stay on the agenda, even if the rest of the proposal does not.