Would an airline be willing to let me board a similar flight that leaves a few hours earlier, if I ask at the airport a few hours before the flight?

I have done it but there was a good weather reason for the change. Notably, the agent said it was allowed because the flight change wouldn’t get me to my final destination any earlier.

It depends on whether you’ve got hold luggage

At this point I was at the terminal after passing through passport control and security.

At this point your hold luggage, if you have any, is on its way to be loaded on the plane. After the Lockerbie bombing and various other similar incidents, airlines are very sensitive about trying to ensure luggage doesn’t fly without its owner on the same flight, to the extent that if a passenger is removed from the plane for any reason, the plane will be held on the tarmac until their luggage is also removed.

So if you have hold luggage, you’re out of luck. The airline categorically will not change your flight on request, because they can’t easily swap over a bag which is likely already on a truck to be loaded.

If you only have carry-on luggage, you might get away with it though.

Yes, and you can always ask. I’ve done it (on SAS), but then they only released the seats on the earlier plane like 30 minutes before departure and you had to be ready and queueing at the gate to see if there were any seats available just before departure.

Some reasons for why they can let you do it is that:

1. they reduce risk of delays, if you are about to board a plane that
   is already known to be on time and on the tarmac. And if your
   original plane is already delayed that’s a certain.
2. If the later plane is full or near capacity, they have a slim possibility so sell more tickets if they increase capacity on a plane that will have more time to sell tickets.
3. Just plain customer service. (More likely in the case of a full service carrier(?))

It obviously depends on the airline. They may even suggest it.

(Back in the late 90s, I arrived at my gate, and the employee at the counter mentioned that another flight would be departing for my destination shortly, from the same gate, and asked if I wanted to transfer to that one. My luggage would be on my booked flight either way.)

I have successfully changed flights in the past. My scenario was flying out of a major east coast USA airport with a winter storm approaching. Our outgoing flight was running late due to the incoming aircraft being delayed in flight. We had arrived early at the airport and I saw another flight to the same destination was in the boarding process. Once the boarding rush was complete, I politely asked at the check-in counter, and was able to switch to the earlier flight since they had seats available. A lot of this was because we had no checked luggage to deal with.

Thankfully we were able to get on this earlier flight, because our original flight was delayed so much due to weather that we wouldn’t have made our connection at the next airport. This would have left us needing to find overnight accommodations there, and because it was a weather delay I’m sure we would have had to pay for it ourselves.

Would there be any point in asking the Wizz air worker in charge of boarding if I could get on the other flight instead of mine?

Absolutely. You can certainly ask.

Is there any chance that they would agree to let me on (even for a small fee)?

Yes. That’s definitely something within the discretion of the gate agent.

The chances of actually getting a seat are all over the place and depend on

1. Internal airline policies. The gate agents have a fair bit of discretion here.
2. To what extent the airline is "at fault" and whether they may have to pay compensation for a delay
3. Fare class of ticket
4. Your Status with the airline
5. Availability of seats and fare classes for these seats
6. Check baggage or carry on only
7. Mood and attitude of the agent you are talking to
8. Etc

If there is a non-trivial delay in your original flight, your chances of them considering it are pretty good especially if the delay would trigger compensation. In general you need to be decisive and fast. Most other people on the plane will have the same idea and if you are #20 in line for 10 open seats, you are not going to get it. You can try at your gate but it’s better to try at the gate of the flight that you want to change to. If there is a long line, you can also call or try online.

Personally I had mixed result with these type of requests. Sometimes it works, sometimes it doesn’t, but there is certainly no harm in trying.

It depends a lot on the airline and the fare.

With a full fare on an incumbent airline, it’s very likely you could be transferred to that flight, especially in your situation (original flight delayed, same destination city, no checked luggage), as long as there are free seats and boarding isn’t finished.

In other situations it’s a lot more variable, especially after check-in. There could be a fee for the change, or a fare difference to pay. Some airlines just won’t do anything at the airport, it’s call center or nothing, others are more accommodating. The closer you get to gate closing time the dicier it becomes because they’re in a hurry, so better to ask before boarding starts.

One thing is certain: it costs nothing to ask. Remember to bear your biggest smile, be polite, don’t take it for granted that you should be allowed to change or change for free, and anything can happen, whether it’s airline policy or just the agent being more helpful than they need to.