It could have done. These engines run hotter than a watercooled engine and any additives in the oil tend to be affected by the extra heat.
This can sometimes lead to a blocked filter due to the addative getting 'stuck' in there.
Check your oil level again to make sure it wasn't overfilled and just for a few miles take off the breather pipe from the air filter box so that any oil coming through won't get into there. Try it then to see how i runs.
The spark plugs could have been contaminated with oil so a quick clean wouldn't do any harm but they should clean themselves after a mile or two anyway if it's just oil contamination.
I'm guessing your air filter is a bit soggy too now! Again, take out and run for a while. Remember to replace these parts asap though after a run. Just make the changes as a temp fix to make sure the engine is ok.
There could be an underlying cause of oil in the filter box ie. high crankcase pressure due to blow by around the piston/rings causing oil to be pushed up the breather stack and through the breather pipe. Check to see how much air is being blown through the breather pipe when the engine is running. Shouldn't be any more than a very gentle blow of air coming through.
Meanwhile... Have fun cleaning your filter box!

Mark.
I'm Not A Complete Idiot... Some Bits Are Missing!
1.6 Modified CT engine.