I had to make the same decision last year, and did this:
(Long answer)
1. Cancelled 3G contract, bought PPDBs
2. Bought 3G HSDPA modem (E272, excellent modem, esp. with Huawei's own software instead of VMC!)
3. Bought Billion HSDPA router, with wireless and ADSL
4. Struggled with increasingly poor performance of 3G (that's where pre-paid really works - you can switch from VC to MTN by the hour while their respective services flounder. I have a SIM card farm next to the modem - 1 VC and 2 MTNs!)
5. Gave up on 3G and installed 4mb ADSL. Took less than a week to get up and running, works on the Billion 3G router. Now use 3G as failover (has happened twice due to lightning).
Overall I'm happy with this arrangement. My LAN (wireless and GigE) have fast access to the Net, low latency (about 20ms locally, 250ms international). ADSL bundles are cheap and even though I'm paying Telkom monthly for the line it's more than offset by the price and number of data-bundles I use in a month. AND I'm not tied into any contracts.
(Short answer)
Dont renew the contract! Buy PPDBs and watch the broadband space over the coming months. There are miles of fibre going into the ground at the moment and there will be new offerings.
BTW - if you're think of renewing to get a better modem, rather buy a good used one (look on gumtree.co.za). There are usually some bargains there, and people will take offers. I put a HSDPA modem there and it still hasn't sold (maybe because no-one wants PCMCIA!). As for getting good deals on laptops and netbooks with a contract - dream on! They're usually out of date by the time you get them, and they're really not cheap either. You can do much better deals elsewhere.