Do you see any major threats in the near future regarding the Litecoin minning with powerfull machines? Is there any other better minning approach for an investment around $10k?
Litecoin's internal difficulty adjustment will always marginalize profitability.
ASCI does not pose any threat to Litecoin or other altcoins, it only presents a threat to small miners using GPU farms as their shares will be minimized.
If you want to invest $10K in mining equipment, I would suggest mining an ASCI resistant coin like Goldcoin (GLD) and then to mine and hold the coins for a couple of years. While your mining help out in the community and contribute to the coin's success.
That's what decentralized currencies are all about.