A few thoughts:
1. Modern boats, properly equipped, can be single or double-handed into the 40' range within reason. If you plan to cross an ocean, then single handing takes on a different meaning than single handing on an afternoon sail. But that's a different topic handled elsewhere on Sailnet.
2. As breezin says, the boat will be slower in it's reactions. That's good and bad. Good because you have more time to pull off a maneuver. Bad because you can't get out of a situation as fast..... you can't just snap the wheel over and expect to avoid a piling, boat, etc.
3. The boat is heavier, probably by a factor of about 2 or more. This means that beyond being a bit slower to react, don't expect to be able to stop a boat by hand when docking or to avoid a collision. You'll need to plan your actions and use your sails, engine, lines, to to the work.... it's a seamanship thing. Planning what you do before you do it is probably the single biggest lesson to learn when moving up in size.
4. Don't underestimate cost as follows:
4a - Lines are heavier and longer.
4b - Ditto for the ground tackle upon which you life may depend. Since the boat is heavier, so too will the ground tackle.
4c - You'll need more life jackets, etc.
4d - Slip rental may go up at your home marina. If you cruise, transient slips will be more.
4e - Insurance may double
4f - Single handing? Buy an autopilot (~$1200 for a tiller or wheel model) 4g - Intellectually, the costs are understood, but that cheap halyard for the 25' boat will be another story when the line goes from 60' @ $.60 to 100' @$1.10
5. A larger boat generally means better creature comforts below.... which means more systems like pressure water, refrig, A/C, etc... more maintenance costs and/or time.
6. Greater responsibility due to more guests? You may end up taking out more guests because of the greater size. It may sound trite and obvious, but the moral responsibility really hits home when you look at a boatload of kids and have to make the decision to return to port because it's blowing too hard FOR THEM, even though they want to stay out.
7. The good news? Better sea handling, better stability, faster, more comfortable, more confidence during a blow, greater cruising range.
Finally - don't make such a big jump without spending some time away from the dock in a boat of the size (and preferably brand) that you expect to buy. I don't mean a 60 minute checkout sail around the harbor. Try chartering a boat for a week or weekend. Spend some time on a friend's boat. Try tacking by yourself. The differences will be obvious.
We've all made the jump to ever larger vessels and it's a natural part of life on the water. Seamanship skills develop for those sensitive enough to care, the costs become manageable as we become used to them. It's forums like Sailnet that help us to become aware of that to which we were oblivious. To me boating isn't something that you learn and do. It's a lifestyle, a learning experience that only ends when you die or sell the boat.
Sabre 38 "Victoria"