Urgent Help: Wire for dedicated lines???

Hi,
Can I run 30A line to a receptacle 20A? Asking this because the cost for 30A and 20A is the same, and I already had Wattgate 20A. Moreover,I can use 30A for a bigger amp in the future.
Some suggest use second ground rod for dedicated lines, others say that tie the dedicated ground to the main ground rod, and then improve the main ground rod. Which way should I use? Electrician suggest a second ground rod for dedicated line. However, the distance from the first and second rod is just 2' apart. Are they too close?
Thanks
Tran

Infwgf, do you know the part number of the 10awg shielded belden cable and where can I find it? Is it available on website?
Thanks
Tran