We are going to our local racecourse for a day at the races, and I have hired a private function room overlooking the track with food provided. It is on Saturday the 31st of March but we will not know the exact time until about a week before, as race times are not finalised until then.
We were thinking of getting everyone to meet at the entrance so we can give them their special members tickets that get them access to our special room for the day. Also we want them to dress up in hats and fascinators etc.
After the races we are planning on continuing on to dinner at a restaurant nearby.

Not wanting the invitations to be too wordy, but would love it if they were cleaver and fun.

Thanks in advance!

I agree, you want to avoid being too wordy, as the information you really need people to know can get lost in there. And you do have some extra info for this event.

But that also happens with clever, cute, or original wording, too. So don't go overboard there, either. After all, it's about the party, not the invitation.

I might do something like this:

***
A Day at the Races
in honor of
Muriel Throckmorton's 50th Birthday

Please join us for [dinner/lunch/light refreshments] and an afternoon/evening of ostrich races
date
time
Ben Hur Race Track
address

Please pick up your special tickets to the party suite at Entrance B
---
Dinner to follow
Chez Ritzy
address
---
Kentucky Derby attire

RSVP: copperearth@whatever.com/123-4567 [whatever you want them to use]
***

"Kentucky Derby attire" was my best shot at suggesting hats without getting too specific and bossy. If you aren't in the US, maybe "Ascot" or whatever a well-known venue where the women wear hats and fascinators would be.

Yes, I did put "50th" in. I hate when people simultaneously celebrate someone's birthday and insult them by saying something like "special birthday" instead of the year, implying that their age is something to be ashamed of. (And, yes, I am over 50!) Either "50th Birthday" or just "Birthday," just please not "Special Birthday."