I have a similar problem with that. I have hundreds of spiders and most settings of them are the same, several are customized. Here is my solution.
First, make a spider_settings.py file:

project_name = 'xxx'

downloader_map = {  # you can list all your downloadmiddlewares here with a alias
    'json_check': (201, 'xy_spider.middlewares.MustJsonDecodeMiddleware'),
    'abuyun': (202, 'xy_spider.middlewares.AbuyunProxyMiddleware'),
    'charset_change': (203, 'xy_spider.middlewares.CharsetSwitchDownloaderMiddleware'),
}
pipeline_map = {  # 0-1000
    'print': (301, 'xy_spider.pipelines.printPipeline'),
    'merge': (1, 'xy_spider.pipelines.MergePagesPipelineForNews')
}


class CommonSettings:
    def __init__(self, **kwargs):
        kwargs = kwargs or {}

        _downloader_mids = {'xy_spider.middlewares.XySpiderDownloaderMiddleware': 200}
        for k, v in downloader_map.items():
            if k in kwargs and kwargs[k]:
                _downloader_mids[v[1]] = v[0]

        _pipeline = {  # here are the pipelines necessary for all spiders
            f'projects.{project_name}.pipelines.MySQLPipeline': 300,
            f'projects.{project_name}.pipelines.MysqlQueuePipeline': 901,
        }
        for k, v in pipeline_map.items():
            if k in kwargs and kwargs[k]:
                _pipeline[v[1]] = v[0]

        timeout = kwargs.get('timeout', kwargs.get('DOWNLOAD_TIMEOUT'))
        self._settings = {
            'LOG_LEVEL': 'INFO',
            'SCHEDULER': 'xy_spider.redis.expire_scheduler.ExpireScheduler',
            'DUPEFILTER_CLASS': 'xy_spider.redis.expire_dupefilter.ExpireDupeFilter',
            'DUPEFILTER_EXPIRE_DAYS': int(kwargs.get('expire', kwargs.get('DUPEFILTER_EXPIRE_DAYS', 7))),
            'SCHEDULER_PERSIST': True,
            'SCHEDULER_FLUSH_ON_START': bool(kwargs.get('get_all', True)),
            'DOWNLOAD_DELAY': int(kwargs.get('delay', kwargs.get('DOWNLOAD_DELAY', 1))),
            'CONCURRENT_REQUESTS': int(kwargs.get('thread', kwargs.get('CONCURRENT_REQUESTS', 10))),
            "SPIDER_MIDDLEWARES": {
                'xy_spider.middlewares.RandomParamFilterSpiderMiddleware': 200,
            },
            "DOWNLOADER_MIDDLEWARES": _downloader_mids,
            'ITEM_PIPELINES': _pipeline,
        }

        if timeout is not None:
            self._settings['DOWNLOAD_TIMEOUT'] = int(timeout) or 20

    def __call__(self):
        return self._settings

Second, you can now customize your settings easily by create an instance of CommonSettings() in your spider class like:

class TestSpider(scrapy.Spider):
    name = "test"
    is_test = not on_server
    _settings = {
        'delay': 1,
        'json_check': 1,
        'timeout': 10,
        'thread': 1,
    }

    if is_test:
        _settings['print'] = 1
    else:
        _settings['get_all'] = 0

    custom_settings = CommonSettings(**_settings)()