I was thinking exactly this myself yesterday.
I'd estimate roughly a break even for the club. There will be extra cost in terms of stewarding etc, which may be offset by extra advertising revenue from the LED perimeter boards (one of the benefits of such a system over static boards) and possibly some extra F&B revenue, although I'm not 100% on the deal with Farrs, so I think any contribution would be negligible, if at all.
The major benefit is hopefully giving the casual fans a good game and a good day out, to entice them back again. I hope there are enough catering staff and the stewarding is mindful of the fact that there will be a number of people who may not know their way around. I also hope it stays dry and warm, as the stadium is an awful place on a wet, windy afternoon, and we will always be pushing water uphill trying to entice people to come, and then to return. Lastly, I hope we have a good atmosphere to match the good attendance, as that also helps encourage people to return.