After the additional overhead of 802.11a, it only get 69 Mb/s (nice number, eh?) Also, 802.11b+ just uses compression, there’s no increase in data rate over regular 802.11b and definitely no latency difference. There’s also no capacity difference, an 802.11b and an 802.11b+ practically max out at the same (low) number of users. Tha’s the big reason to switch to 802.11a.
And, yes, any good WAP or Router+WAP comes with a control program, and there are ways of ensuring no evesdropping such as 128 bit WEP, which would still take over 1 billion years to brute force all of the keys. You can even write own the WEP code (I do) and stick it in a drawer that’s physically secure. In addition, all of the good wireless NICs and wireless routers support WEP in hardware so you don’t take any performance penalty for it (this is different than just supporting WEP, btw, and most NICs that list it in hardware actually don’t do it … AFAIK only 3com and Intel do it in hardware).