I continue to feel strongly about the benefits of cross-training, especially as we age, but if you want or need to be good on the erg, you have to spend time on the erg. A minimum of three days a week is a must, but four would be better. What you do on the erg depends on what you're training for. Will you be racing 2K at an erg competition? Is the coaching asking for a 6K time to help determine boat lineups?
Whatever the answer, I would vary my workouts, doing some short, some mid-, and some longer length pieces - but however you approach it, if your training isn't doing what you need it to do, you don't want to find out on test day.
One of my favorite workouts for tracking progress, in this case in preparation towards a 2K test, is 4 x 500 meters with 1 minute off in between. This workout would be done for the first time six to eight weeks out from your erg test. Ten days to two weeks later do the same workout, but now with only 45 seconds rest in between. Another 10 days to two weeks later, repeat the session with 30" rest, then 15" until you're ready to do it with no breaks.
For people that are fairly new to the erg, it's a great way to work on pacing. The 500 meters should be done at the pace you're looking to do your 2K. So if your goal is 8 minutes, then each 500 is done at 2:00. The first piece should be with a start, and you can experiment to find out what works best for you. A few short strokes to get the wheel going, ten high then settle in - or are you better at going 20 high? The 2nd and 3rd pieces should be about getting right to pace and holding it there as easily as you can. On the 4th piece, add a sprint. Again, experiment to figure out what works best.
This workout will also help psychologically, as you can literally see yourself holding these splits, making it easier to believe you can reach your goal.
If you're training for a 1K or a 6K, the workout can easily be adapted by doing 4 x 250 or 6 x 1K. Pacing is particularly important on the longer pieces. While you might be able to get away with a bit of fly and die on a 1K, it won't work on a 5- or 6K.
Time on the erg will help train your mind and body specifically for an erg competition, so if that's your goal, get on the erg now!
Smile or grimace? Doesn't matter, you still have to get on the erg!