I hear you! You don't want purses on the credenza, but you don't want to be bossy or inhospitable.
Honestly, I think even giving them someplace else to put stuff isn't going to work. Someone will slip past you, or later they will get their bags for some reason and then put them on the credenza. And knowing you, I suspect you won't feel quite as gracious as I know you like to be no matter how you word it.
People re always plunking their bags down in the kitchen when they come. Drives me nuts, because I'm probably about to put appetizers out on the table (I'd have them out before they come if I could trust the pets!), and the counter is even worse, because I need that space to work, and now I have to not only remove the bag but clean the counter, because the bag has probably been on the floor someplace (that's where I'm probably going to put it). So when I am the guest, I try to remember to put my bag on the floor behind some chair or between staircase balusters or something. Then I know it's not in the hosts' way, and as a bonus for me, it will be there when I want it, because no one will have had to move it.
I think your best bet is either a piece of glass or else putting a runner on when people come. Like rolling up or covering your pretty front hall runner on wet days, putting away breakables before large parties or children's visits, or for that matter having a tablecloth covering your lovely dining table for a dinner party.
It's disappointing that some of our prettiest things can't be on display, or on display the way we think they look best, exactly when we most want our homes to look their best. But that's the way it is.
May it always be your worst problem!