I have entered 4 and still have a level 4 ticket, a level 2 ticket and a level one ticket. They take forever to fill up so that is a downer. I should look and see if they have an expiration date on the tickets. I played in them to help me with multitableing. I haven't play in one for a while but i doubt much has changed.
You should have no problem in the early levels and since the top six in every level gets something they are not that hard to get a lot of experience for a small price. I just think it is a lot of work for a reward that will take you a long time to collect.