To share my experience with you.
Last year July I did add RM20 to change from older decoder to beyond for my parents. The RM20 included some additional chinese channels and Astro on demand.
For me there seemed to be conspiracy for making us change... after astro started promoting beyond HD, we started to get more and more lousy signal with theolder decoder. Some nights with clear sky clear moon no rain, we cannot receive any signals at all, or the signals kept breaking off. My parents were frustrated. I called Astro help line and of course they always started off with some retarded instruction like, plz power off and on the decoder, take out the smart card and reinsert bla bla blah but it won't work. If want to send astro technician over need to add rm50 and some additional charge if need to change decoder or watever. Then they started to promote the conversion to HD with no additional installation charge. At first I rejected that idea. But as it continued for a few days with no consistent signals, I decided to just change it, partly thinking alright, maybe my parents can watch in HD, better also.... so I changed...
Turns out most chinese channels that my mom tuned in to, were NOT in HD

On the other hand, when my dad watch sport channel, he still always switch to non-HD one even though I told him many times that there are HD sports channels~

ok this part is human issue, haha.
Since then I think Astro is slowly transforming more channels to HD, but I still need to remind my parents now to stop tuning to the non-HD one.
Last month I grabbed the Astro FOC offer to change the beyond to PVR. Enjoying it right now. finally I am at peace with the decision

so are you paying anything additional to your bill while using old decoder? or are you paying extra RM20?