It's not going to hurt you to do all the things that jbarlow and David suggest, but let me try to make things a little bit easier for you (or maybe harder, because I'm going to say you can probably get away with a lot of things, but I'm not going to promise).
A classic rule of thumb is that you can consider a circuit to be a lumped circuit if none of it dimensions is longer than 1/10 the wavelength of the highest frequency signal of interest. If it's a lumped circuit you can consider your tracks as just connections between discrete elements. If its not a lumped circuit you need to worry about distributed circuit effects, and consider your traces as transmission lines.
You're talking about a clock frequency of 30 MHz, corresponding to a wavelength of 10 m. If propagating through FR4, this wavelength will be reduced to about 4.7 m. And a circuit length of 40 cm. So for the fundamental of the clock signal you're right on the edge of the old rule of thumb.
Problem: You don't just have to worry about the clock frequency, but how many harmonics of that frequency need to be transmitted to give the rise and fall time you want. If you deliberately slow down the edges you transmit you can probably get by with just the 1st and 3rd harmonics (David alluded to this when he mentioned not necessarily using maximum drive strength).
This gives you a maximum frequency of interest of 90 MHz, and corresponding wavelength (in FR4) of about 1.6 m. So the critical distance is 16 cm. That means that overall you want to provide a closely coupled return path, deisgn your tracks as transmission lines and terminate with an appropriate impedance, etc.
But you probably don't have to pay extra for controlled impedance. If you design with traces above the minimum width available from your vendor, (say 8 or 10 mil), the normal tolerances will most likely give you adequate performance.
And if along the way you have to go through a via, or run over a short gap in the ground plane, or you can't put a bypass capacitor right next to a load part, don't sweat it too hard. If you want to run your tracks straight from connector to connector, with a few cm stub to reach the load chips on each board, it'll be okay. If the length of the uncontrolled part of the path (or the slot in the ground plane) is less than a few cm, it's not going to ruin your day. Even if it's 10 cm, you're likely to get away with it, but don't push your luck.
For example, this means when you connect between boards, there's no need for a high-cost impedance-controlled connector. Even a couple of centimeters of ribbon cable will be fine. A ground-signal-ground or ground-signal-signal-ground pattern of wires in the ribbon is a good idea, but don't worry about impedance-matched twisted pair cables or coax.
For another, if you do decide to use a buffer on each board, that would enable you to pretty much treat the circuit on each board (at 10 cm length) as a lumped circuit. You will want to manage the buffer skew, as David described, and you'll have to limit the rise and fall times out of each buffer, but you'll gain a lot of flexibility in layout on each board without degrading functionality. That said, the more you do to keep your return paths close to your signal traces, the less likely you are to have a nasty surprise when it comes to EMC testing.