This is the thing. We can use math to find out how much it would take to travel all these distances. To flyby Moho, and approach at its apoapsis (which is possible due to its argument of perigee), we can use a delta v map to find an intercept with moho takes 1690 m/s from LKO. If you wait for a long, LONG, LONG, LONG, LONG amount of time in game, you MAY be able to get an intercept with Kerbin again without another drop of fuel. Then, if we assume that Moho and Dres are on the same plane (which they are not) and that you will hit Dres' trajectory at periapsis (you probably won't), we can use vis viva to find that that takes 1806 m/s in an absolutely perfect world. Using the same assumptions as last time, we find that an Oberth to Eeloo takes 1444 m/s.
It is needless to say that this arrangement is impossible due to the way the planets are laid out in the game.
Adding the numbers gives 4940m/s. Even though that may sound relatively small, basically ALL of these planets are on different planes, so much say that it is easily safe to say that you may need a 80% margin for orbital maneuvers, boosting it up to 8500m/s. Another cost you will have to pay dearly for is time. You are going to waste so much time, both real time and game time to go to a few different planets, that it is LITERALLY easier to build a completely new rocket.
The d/v may sound like chicken scraps; afterall, that is how much is needed for a duna mission. Remember, though that you need a separate lifter stage to get your Duna rocket into orbit. And without mods, it is even harder.
It is up to you, to make the decision now.