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Reg,
Due to seeing conditions, transparency, thermal currents in your tube and not having your mirror at ambient temperature, it's actually very rare that you'll use an eyepiece that gives you magnifications of 200x or over.
It's not so much the type of eyepiece (series 500 or a nagler) that limit your view of detail on the planets, it's those factors described above that are the major influence.
In my 10" dob, my main planetary eyepiece will be (soon to be purchased) a 6 or 7mm eyepiece, which will give me 208x on steady nights. When the seeing is not good, I can only use a 9mm, which only gives me 138x.
On above average nights, I'll be hoping to use a 5mm which will give me 250x. So you can see that it's just not possible to use high magnification on the planets 99 nights out of 100.
So while a better eyepiece will help you see detail when the seeing is good (better contrast, light transmission, colour reproduction, edge performance), don't try and push the magnification too high, as all you'll get is a wobbly blurry bubble.
Also don't forget that Mars is shrinking fast, less than 11" now and it's very difficult to see detail on something so small. You should try Saturn, rising around midnight and high enough to view by around 2am. On a steady night you'll see the cassini division almost all the way around, banding on the globe, it's an awesome sight.
And don't forget our nearest neighbour, the moon! Plenty of fine detail to see on the moon and can be observed at different times throughout the month so it's always convenient (except at full moon!)
Hope i've helped!
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