Leveling rate issues, alt. XP, variant options?

So!
I'm playing in a great game of DW, using Vincent Baker's Seclusium book.

It turns out the seclusium I made provided a ton of play (the players have been in and around it for about 6 3-4 hour sessions, maybe? although actual serious playtime is closer to 2 hours / session probably).

Anyhoo, in this time (only one real "adventure" and a little exploration of the nearby world), the characters have advanced pretty rapidly! My highest level PC is, I think, 7th level, and most are 4-6.

So, it seems to me that a given adventurer getting *maybe* two-three adventures before hitting the level cap... well, it just seems poor to me!

I expect the players will want to keep playing the same characters, but it feels kind of stale without further advancement.
The options there are: play two characters, retire and start anew, and change classes. Right?

Playing two characters is fine, I reckon, but in an already large group (5-7 players) I can see it being a book keeping and attention nightmare if everyone does it. Retiring prevents the above goal of playing the same character, and changing classes is only sometimes a good option.

So, what is to be done?
1) Slow XP gain
2) Remove the level cap
3) ...something... else?

1 is fine for my purposes, but I feel the players might not be overjoyed about slower leveling. It does remove a bit of the "shiny new stuff" excitement as well as a tiny bit of the feedback loop.
2 is not so great. Eventually you just end up with PCs with every advancement (a book-keeping annoyance anyway, and kind of boring) and +3 on all stats. Meh!

So... what other options are their? Have others run into this problem?
I think the ideal "career" for an adventurer is 1-3 "big" adventures (like my seclusium or bigger), and 2-5 small/medium adventures, before retiring or what have you.

(Actually, really, "adventure" here is more a shortcut for "dangerous locale to explore, possibly with some situation going on")

Any suggestions?

- Alex

I would say there are a few ways to go here. 

1)Decrease the XP that players receive at the end of the session.  You can do this by eliminating XP points for failures (I actually like this rule a lot as it is kind of a consolation prize and makes failure a LOT more palatable).  You could only give 1 XP point max at the end of the game for all the things they ask (learning about the world, completing a bond, etc).  I like this idea less than the next one.

2)Increase the amount of XP it takes to go up a level.  I kind of like this idea better.  Instead of Level+7, make it Level+(7+Level).  XP requirements to go up levels steps up each time higher and higher (twice as much, actually) but you still get to give rewards for completing bonds and rolling failures. 

Just my 2 cents. 

Third option: give them something to spend xp on during play. An obvious choice is "spend an XP to get +1 to a roll you just made." That actually has an even greater impact than just the spent XP, because it also reduces XP from misses.