That really depends on a lot of factors:
1. Your preferences - if you like taking photos then the L1020 is a must-have, but you must check the status of the camera
2. The status of the L1020 - it's older; hardware and accessories are harder to find; has it been dropped; has it been repaired before; try the actual device first before deciding
3. The status of your L730 - has it been dropped; has it been repaired before;
4. Personal intentions - check the intentions of your cousin; ask him why he wants your L730 for his L1020 - observe his phrasing, body language, tone, etc. Ask him if he frequently drains the battery below 50% (important for battery life for old devices).
From all of these, you should be able to reach a sound decision - we won't decide for you.
P.S.
If your cousin took good care of the L1020 (better than how I took care of mine after around 1.5 years of ownership), then I'd take it right away. My L1020 has been repaired once, has been dropped on a soft surface from around 12 inches (not major), has barely visible hairline scratches (you need a really bright flashlight to see them off the reflection), and has one minor ding near the SIM tray.