That's a good time to be there, although it will probably be pretty warm and humid. If you ever head up there and can plan it around the Allentown Art Festival or any other number of lesser festivals, that would be best. There's a couple Andrew Lloyd Wright homes up there to tour and some Olmstead parks. A lot of architecture downtown, but not much else. Last time up I toured a Wright home on the lake that had fallen totally into disrepair and is being restored. I enjoyed it, but not for everyone's interests.
Save this away somewhere for whenever you are in town, because I know how you operate. I need to give you one word of warning about Beef on Weck. When you look for the "best beef on weck" you're going to hear Schabl's in West Seneca. And it looks the part. But by and large, their beef on weck sucks and is highly overrated. Make the trip out to Swistons Beef & Keg instead, on the Erie Canal in North Tonawanda. Dank, dark bar with only two food items on the menu...beef on weck and chili. And complimentary stale popcorn. The atmosphere is good, beer is cold, and the beef on weck is fantastic.
Most of Buffalo's signature food items are great almost everywhere. It's definitely worth going for the Anchor Bar for wings because of the history, or La Nova for pizza with it's mob history. But honestly, pick any pizza place or bar, and you'll have to get pretty unlucky to get something less than excellent. There are a few dogs here or there, but most places serve those items almost indistinguishable from the "famous" places.
But beef on weck...that's different. There is a lot of bad beef on weck out there. Everyone thinks they need it on the menu, but honestly, it's not that easy to do right. Roast beef doesn't stay fresh that long, and weck rolls only last about six hours before they start to go bad because the salt melts. There's a good chance you'll be getting some sliced Boar's Head microwaved and served on a warmed up month-old weck roll they pulled out of the freezer. Every neighborhood or area probably has their own great place, but they've also got dozens of bad ones. Unless you get a personal recommendation from someone up there, I can vouch for Swistons for sure, awesome combination of beef and atmosphere. If you can take a pass on the atmosphere, Charlie the Butcher will give you a reliable sandwich.
For the other stuff...wings, pizza, char-grilled hot dogs, texas hots, greek food, polish, italian etc...if it looks good (especially if it is old and hole in-the-wall-y), it probably is. Although I would be happy to give recommendations for anything.